a) is an explanatory diagram showing the manner in which the absolute sensor is attached in the gear-equipped motor in
Embodiments of a reduction gear unit in which the present invention is applied shall be described below with reference to the drawings.
The reduction gear unit 4 comprises a cylindrical unit housing 5, and a reduction gear 7 is coaxially incorporated in this unit housing 5 on the side of an input-side open end 6. The reduction gear 7 is a cup-shaped wave gear device that comprises an annular rigid internal gear 71, a cup-shaped flexible external gear 72, and an elliptically contoured wave generator 73. The rigid internal gear 71 is screwed in and fixed to the internal peripheral surface of the input-side open end 6 of the unit housing 5. The cup-shaped flexible external gear 72 is disposed so that the open side faces towards the motor unit 2, and an output shaft 8 is integrally formed in a coaxial manner on a cup-shaped bottom surface portion 72a of the external gear. The wave generator 73 is coaxially connected and fixed to the distal end of a motor shaft 31 of the motor unit 2.
The flexible external gear 72 is bent into an elliptical shape by the wave generator 73, and the two end portions of the major axis of the elliptical shape mesh with the rigid internal gear 71. When the wave generator 73 is rotated at a high speed by the motor unit 2, the meshed positions of the gears 71, 72 move in the circumferential direction, and a reduced rotation corresponding to the difference in the number of teeth between the two gears is outputted from the flexible external gear 72. As a result, the output shaft 8 integrally formed on the flexible external gear 72 as a reduced-rotation output element also rotates at a reduced speed.
The output shaft 8 extends up to an output-side open end 11 of the unit housing 5. An output-side bearing 12 is disposed on the inside of the output-side open end 11, and the distal end portion of the output shaft 8 is rotatably supported by the output-side bearing 12. The output-side bearing 12 comprises an outer ring 13 screwed and fixed to the internal peripheral surface of the output-side open end 11 of the unit housing 5, an inner ring 14 screwed and fixed to the outer peripheral surface of the output shaft 8, and a plurality of balls 15 that are rollably inserted between these two rings. In the present example, an annular mounting flange 16 that protrudes towards the output side is integrally formed on the inner ring 14 fixed at the distal end of the output shaft 8, and a member on the load side (not shown) is connected and fixed to the mounting flange 16. An annular protuberance 18 is formed on the output-side end surface 17 of the unit housing 5 so as to encircle the mounting flange 16, and an oil seal 19 is attached between the mounting flange 16 and the annular protuberance 18.
An absolute sensor 20 is disposed inside the unit housing 5, between the output-side bearing 12 and the cup bottom surface portion 72a of the cup-shaped flexible external gear 72. The absolute sensor 20 is provided to sense the absolute rotational position of the output shaft 8 in a single rotation, and the absolute sensor comprises a bipolar-magnetized magnet ring 21 and two Hall elements 22, 23. The Hall elements 22, 23 are attached to a flexible printed circuit board 24 that is bend into an arc shape.
A sensor having four Hall elements can also be used as the absolute sensor. Such use is effective for reducing the formation of erroneous components in the sensory signal waveform by the axial wobbling of the output shaft 8.
Next, the configuration of the motor unit 2 will be described with reference to
An annular mounting flange portion 36a that protrudes forward and outward is formed integrally on the front end surface of the external periphery of the front side end plate 36 of the motor housing 35. This mounting flange portion 36a is coaxially connected and fixed to the input-side open end 6 of the unit housing 5 of the reduction gear unit 4.
The magnetic encoder 40 is magnetically separated from the motor main body side by a magnetic shield disc 41 attached to the rear surface of the rear-side end plate 37, and the encoder has a bipolar-magnetized magnet ring 43 that is attached to an attachment disc 42, which is coaxially attached to the back end portion of the motor shaft 31 protruding backward from the end plate 37. A disc-shaped substrate 44 is coaxially disposed facing the rear side of the magnet ring 43, and an MR sensor 45 and a Hall sensor 46 (see
With reference to
The Hall sensor 46 is mounted on the front surface of the substrate 44 at a region facing the ring magnet 43. The Hall sensor outputs a detection signal having one cycle for one rotation, which varies in a sinusoidal manner in conjunction with the variation in the flux intensity of the rotating magnetic field.
Next, the substrate 44 is bonded and fixed to the inner side of a sealed end surface 47a of the encoder case 47. This is advantageous in making the magnetic encoder 40 smaller and more compact, because less space is needed to attach the substrate than in cases in which the substrate 44 is attached with screws or the like.
An arcuate wiring window 47b that extends to, e.g., 120 degrees, is opened in the sealed end surface 47a of the encoder case 47, as shown in
In the reduction gear unit 4 of a gear-equipped motor 1 configured in this manner, an absolute sensor 20 for sensing the rotational position of an output shaft 8 is disposed between the output-side shaft bearing 12 inside the unit housing 5 and the bottom surface portion 72a of a cup-shaped flexible external gear 72. The two Hall elements 22, 23 of the absolute sensor 20 output signals that are out of phase by 90 degrees and have one cycle per rotation of the output shaft 8. The absolute rotational position of the output shaft 8 can be sensed on the basis of these signals.
The portion of the output shaft 8 on which the absolute sensor 20 is disposed is supported in a straddle-mounted state by the output-side shaft bearing 12 and the flexible external gear 72. Accordingly, there is no loss of moment rigidity in the reduction gear unit 4 even if this portion of the output shaft 8 is lengthened in order to ensure a space for accommodating the absolute sensor 20.
Next, in the motor unit 2 of the gear-equipped motor 1 of the present example, the magnetic encoder 40 incorporated in the back end portion is configured using the MR sensor 45 and the Hall sensor 46. The absolute position can be sensed within a single rotation on the basis of the Hall sensor 46 output.
The MR sensor 45 is inexpensive, and a semiconductor process can be used to orthogonally align elements with high precision in order to create the two signals. Therefore, the assembly operation can be simplified, output can be adjusted in a simple manner, and costs can be lowered in comparison with cases in which multiple Hall sensors are used to configure an absolute-type magnetic encoder. Furthermore, the structure can be made smaller, more compact, and less expensive in comparison with cases in which a bias magnetic field is applied to the MR sensor to obtain a signal having one cycle per rotation.
Particularly, in the magnetic encoder 40 of the present example, the disc-shaped substrate 44 on which the MR sensor 45 and Hall sensor 46 are mounted is coaxially disposed facing the magnet ring 43. Therefore, this is advantageous in reducing the diameter of the magnetic encoder 40 in comparison with cases in which the magnetic sensor is disposed on the external peripheral side. Disposing both sensors 45, 46 on the front surface (the same flat surface) of a common substrate 44 is also advantageous in reducing the thickness of the magnetic encoder 40. Additionally, since the substrate 44 is bonded and fixed to the encoder case 47 and the connection terminals 48 of the substrate 44 are exposed to the exterior through the encoder case 47, less space is needed for fixing the substrate and laying the wires, which is advantageous in reducing the thickness of the magnetic encoder 40.
As described above, in the gear-equipped motor 1 of the present example, a sensor 20 for sensing the rotational position of the output shaft 8 can be disposed without reducing the moment rigidity of the reduction gear unit 4. The entire length can be considerably reduced in comparison with a motor in which an optical rotary encoder or the like is incorporated, and this length reduction is advantageous in cases of placing the motor in a small location.
In the present example, a wave gear device is used for the reduction gear, but a reduction gear other than a wave gear device, e.g., a planetary reduction gear or the like, can be used. A sensor other than a magnetic absolute sensor, e.g., a rotary encoder, can be used as the sensor for sensing the rotational position of the output shaft.
Number | Date | Country | Kind |
---|---|---|---|
2006-152944 | Jun 2006 | JP | national |