GB2117572A

GB2117572A - Motor with a position sensor

Info

Publication number: GB2117572A
Application number: GB08302542A
Authority: GB
Inventors: Mitsuru Ikegami; Ryuji Toida; Yoshio Hamada; Masayuki Nashiki
Original assignee: Okuma Tekkosho KK; Okuma Machinery Works Ltd
Current assignee: Okuma Corp
Priority date: 1982-03-26
Filing date: 1983-01-31
Publication date: 1983-10-12
Also published as: DE3310564A1; GB8302542D0; GB2117572B; JPH0158745B2; DE3310564C2; JPS58165644A

Abstract

A motor (30) coupled to a position sensor (40), wherein the motor rotor (33) is directly coupled by a taper coupling to the sensor shaft (42), and the motor body is coupled to the sensor body by a diaphragm (32). The diaphragm is substantially rigid in the direction of rotation of the shafts, but is flexible in a direction generally radially of the shafts to accommodate non-coaxial alignment of the two shafts (33, 42). <IMAGE>

Description

SPECIFICATION Motor with a position sensor This invention relates to a motor with a position sensor.

It is known to provide a position sensor on motors. In the accompanying drawings, Figs.

1 to 3 show three known arrangements of motors with position sensors. Referring to these drawings, the motors 1 shown in Fig. 1 is provided with a gear box 2 at the rear end face thereof. The gear box 2 is mounted with a position sensor 3 pf the rotating-shaft type, and the rear end of the rotating shaft 1 A of the motor 1 is connected with the front end of a rotating shaft 3A of the position sensor 3 through gears 4 and 5 in the gear box 2.

Thus, as the shaft 1 A of the motor 1 rotates, the motion is transmitted to the gear 4, then to the gear 5 which is engaged with the gear 4, and finally to the shaft 3A of the position sensor 3. As a result, precise detection of position is impossible due to inevitable backlash between the gears 4 and 5.

The motor 10 indicated in Fig. 2 is provided with a box 11 at the rear end thereof. A position sensor 1 2 is mounted on the box 11 and the rear end of a rotating shaft 1 0A of the motor 10 is coupled with the front end of a rotating shaft 1 2A of the position sensor 1 2 by a bellows coupling 1 3 within the box 11.

The bellows coupling 1 3 is so constructed as to be rigid in the direction of rotation but flexible so as to accommodate any inclination of the shaft 1 2A or 1 OA and any eccentricity of the shafts. The rotary motion of the motor 10 is transmitted in the following order: the rotating shaft 1 OA drives the bellows coupling 13, which rotates shaft 12A, which turns the position sensor 1 2. Although this device does not suffer from the same back-lash problem as the motor of Fig. 1, it tends to wear out quickly in the bellows coupling especially if there is any significant shaft inclination or eccentricity.

The motor 20 indicated in Fig. 3 is provided directly with a position sensor 21 at the rear end thereof. The revolving position of the motor 20 is detected by the position sensor 21, by revolving a rotor 23 within a stator 22 of the sensor 21, the rotor 23 being mounted on the rear end of a motor shaft 20A. Although the motor of this design is free of such problems as back-lash between gears and bellows coupling failure, it does have the disadvantage of being difficult to manufacture. In particular it is extremely difficult to assembie the stator 22 and the rotor 23 without eccentricity, and the rotor 23 (which is an element of the delicate and precise position sensor 21) has to be manufactured integrally with the shaft 20A of the motor, which may be relatively large.

We have now devised, in accordance with the present invention, a motor with a position sensor which does not require gear trains having back-lash or bellows couplings which tend to fatigue and break down, which is still capable of detecting a precise position, and which may be relatively simply manufactured and assembled.

According to the invention, there is provided a motor having a rotating'shaft type position sensor coupled thereto, wherein the motor comprises a body and a drive shaft, and the position sensor comprises a body and a driven shaft, and wherein the motor drive shaft is coupled generally coaxially to the sensor shaft by a taper coupling to transmit rotary motion of the drive shaft directly to the driven shaft, and the motor body is coupled to the sensor body by a flexible coupling which substantially rigidly couples the bodies in the direction of rotation of the shafts, but is flexible in a direction generally radially of the shafts.

In the present invention, a motor with a position sensor is so contructed that the rear end of the rotating shaft of a motor is tapercoupled with the shaft of a position sensor of a rotating shaft type with a bearing and that a coupling element in the form of a diaphragm which has rigidity in the revolving direction and flexibility for inclination or the radial direction is placed between the rear circumference of the motor and the front circumference of the position sensor.

In order that the invention may be more fully understood, one embodiment thereof will now be described with reference to Fig. 4 of the accompanying drawings.

Referring to Fig. 4, a cylindrical box 31 is provided at the rear end of a motor 30 and the periphery of one end of the box 31 is connected with the front end of a position sensor 40 by a coupling element which is preferably in the form of a diaphragm 32. A stator 41 of the position sensor 40 has a rotor shaft 42 mounted on bearings 43 and 44 therein, in a manner to allow revolution of the rotor shaft 42. A rotor 45 for detecting position is provided on the rotor shaft 42, and the front end of the stator 41 is engaged with the inner circumference of the diaphragm 32. The rear end of the rotating shaft 33 of the motor 30 is tapered and the end thereof is connected with the rotor shaft 42 of the position sensor 30 by means of a bolt 46.The rotating shaft 33 of the motor 30 is thus tapercoupled with the rotor shaft 42 of the position sensor, providing a co-axial or close to at an excellent coaxial arrangement in a simple manner. The coupling diaphragm 32 is so constructed that it is rigid in the direction of revolution of the rotating shaft 33 but radially flexible to accommodate slight departures from co-axiallity of the shafts 33, 42.

In operation, as the shaft 33 of the motor 30 revolves, the rotary motion thereof is transmitted to the rotor shaft 42 of the position sensor 40 through the taper-coupling, and the position of the rotating shaft 33 of the motor 30 is detected by the mechanism of the stator 41 and the rotor 45 mounted on the rotor shaft 42. The rotor shaft 42 of the position sensor 40 is rotated on the bearings 43 and 44 provided between the shaft 42 and the stator 41.

Thus, as the motor with the position sensor according to this invention does not use gears, it is free of errors caused by gear backlash. Further, the use of a taper-coupling ensures a close to co-axial coupling thereby reducing errors arising from non-coaxial arrangement and reducing the possibility of breakdown of the coupling element 32. As the coupling element 32 has flexibility in the radial direction, any eccentricity between the rotating shaft 33 of the motor 30 and the rotor 42 of the position sensor 40 is conveniently absorbed by the coupling element 32 through the diaphragm structure.

It is preferable to mount the coupling element 32 at a location as close as possible to the motor, so that the possibility of fatigue and breakdown is minimized and the force applied on the delicate rotor shaft minimal.

The box 31 mounted on the motor is not always necessary. The coupling element may be directly attached to the motor depending on the construction of the motor so that the coupling element is coupled with the position sensor. The rotating of the motor and the rotor shaft of the position sensor may be coupled by any other arbitrary elements.

Claims

1. A motor having a rotating shaft type position sensor coupled thereto, wherein the motor comprises a body and a drive shaft, and the position sensor comprises a body and a driven shaft, and wherein the motor drive shaft is coupled generally co-axially to the sensor shaft by a taper coupling to transmit rotary motion of the drive shaft directly to the driven shaft, and the motor body is coupled to the sensor body by a flexible coupling which substantially rigidly couples the bodies in the direction of rotation of the shafts, but is flexible in a direction generally radially of the shafts.

2. A motor according to claim 1 wherein the flexible coupling is in the form of a diaphragm.

3. A motor according to claim 1 or 2, wherein the forward end of the sensor body faces the rear end of the motor body and the said flexible coupling extends between the adjacent peripheries of the said bodies.

4. A motor according to claim 3, wherein the motor body includes a cylindrical housing at the rear end thereof.

5. A motor according to claim 1, 2, 3 or 4, wherein an end of a stator of said position sensor is coupled to said flexible coupling.

6. A motor according to any of claims 1 to 5, wherein the taper-coupling is effected by coupling the driven shaft of said position sensor with an end of the drive shaft of said motor by means of a bolt.

7. A motor according to claim 4 wherein said flexible coupling extends from the rear end of said cylindrical housing, in a direction generally radially inwardly towards said shafts, to a stator of said position sensor.

8. A motor having a rotating shaft type position sensor coupled thereto, substantially as herein described with reference to Fig. 4 of the accompanying drawings.