METHOD OF FIXING PULSE ENCODER TO MOTOR AND PULSE ENCODER-CARRYING MOTOR

Abstract: A fixed code plate carrying a light pickup element and a pattern of concentric slits is temporarily attached to the end of a motor housing. The housing is then turned about the motor shaft (14) and eccentricity of the slit pattern is referred to in order to centre the fixed code plate. The fixed code plate is permanently fixed to the housing, a clearance gauge being placed on the fixed code plate, and a sleeve together with a rotary code plate is put on the motor shaft and fixed. Alternatively, the rotary code plate is temporarily attached to the sleeve and is rotated to correct eccentricity before fixing.

Description: TECHNICAL FIELD The present invention relates to a method for attaching a pulse encoder to be built in a motor to the motor, and relates to the motor having the pulse encoder attached thereto by that method. BACKGROUND ART A method whereby a rotary coded plate is first attached and then a stationary coded plate is attached on the basis of the rotary coded plate, is adopted in the prior art as a method for attaching the pulse encoder to the motor. Namely, the rotary coded plate is attached to one end of an output shaft of the motor so as to be at a right angle to a central axis of the shaft and centrally aligned. On the other hand, the stationary coded plate is fixed upon a plate member having a recess for mounting a light sensor, by an adhesive agent, and the position of the light sensor is adjusted in two dimensions (in a plane) with regard to the positions of slits of the stationary coded plate, and the light sensor is fixed by screws. A spacer is interposed between the plate element and one end of the motor so that the plate element having the light sensor and the stationary coded plate are separated from said rotary coded plate by a predetermined clearance distance, and the position of the plate element is adjusted in two-dimensional directions so that slits of the rotary coded plate are coaxial with slits of the stationary coded plate, and the plate element is fixed to one end of the motor by screws. Conventionally, a pulse encoder is built in a motor in the manner mentioned above, but it is time-consuming to attach the pulse encoder to the motor in such a manner, and an accurate attachment thereof cannot be efficiently achieved. Namely, a working step is necessary whereby the stationary coded plate is mounted separately from one end of the motor and spaced from the first mounted rotary coded plate by a predetermined clearance distance. This clearance distance must be made shorter as a resolution power of the pulse encoder increases, and thus the adjustment work becomes more difficult. Furthermore, the position of the plate element having the stationary coded plate must be adjusted in two dimensional directions so that the positions of slits of the stationary coded plate are set coaxially with the positions of slits of the rotary coded plate. Examples of known rotary encoders and assembly methods are disclosed in EP-A-0 003 288 and GB-A-2 051 353. EP-A-0 003 288 discloses a method of assembling an incremental encoder by using an especially adapted alignment fixture. A housing is positioned on the fixture to obtain an alignment of a fixed coded plate with the housing. A code plate is mounted on a shaft of a motor using a hub element which is concentric and perpendicular to the axis of that shaft. The accuracy of the three dimensional alignment of the fixed coded plate with the housing depends upon the accuracy with which that portion of the housing formed for mounting the rotor stator has been manufactured and also upon the accuracy of manufacture of the mounting fixture. Document GB-A-2 051 353 discloses an incremental rotary transmitter in which a rotatable pulse disc is mounted on an extension of a motor shaft, and a stationary plate is freely mounted on the same shaft via a stationary sleeve element. The sleeve must be accurately concentric with the shaft and must have a flange portion allowing the stationary plate to be mounted upon the flange portion and to be positioned perpendicular to the axis of the motor shaft. A further sleeve, to which the rotary pulse disc is fixed, is formed to be concentric with and perpendicular to the motor shaft axis. Thus, the two sleeve elements must be very accurately manufactured. DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems by providing a method for building each element of a pulse encoder in a motor accurately and efficiently, and thus provide a motor with the pulse encoder built therein by the above method. According to the present invention there is provided a method of attaching a pulse encoder to a motor using a clearance gauge, characterised by: grinding a housing of said motor to form a plane end surface which is perpendicular to a rotation axis of an output shaft of said motor; fixing a front end of said output shaft of said motor to a worktable in such a manner that a rear end of said output shaft of said motor is exposed within a portion of said housing of said motor; fixing a stationary coded plate of said pulse encoder to said housing plate end surface by a process which includes: temporarily attaching said stationary coded plate to said housing plane end surface such that a circular track pattern on said stationary coded plate surrounds said output shaft axis, rotating the housing relative to said shaft to determine the deviation of the centre of the circular track pattern from said output shaft axis; moving said stationary coded plate to align the centre of said circular track with said output shaft axis, fixing said stationary coded plate to said housing plane end surface, and attaching a rotary coded plate of said pulse encoder to said output shaft rear end by a process which includes: mounting a sleeve having said rotary coded plate attached thereto, on said output shaft from said rear end with said clearance gauge interposed between said stationary coded plate and said rotary coded plate, advancing said sleeve on to said output shaft until said rotary coded plate abuts against said clearance gauge in contact with said stationary coded plate, fixing said sleeve to said output shaft, and removing said clearance gauge after confirming the fixing of said output shaft to said sleeve. Preferably, the process for attaching said rotary coded plate further includes rotating said shaft relative to the housing to determined the deviation of a centre of a circular track pattern on said rotary coded plate from said output shaft axis, moving said rotary coded plate on said sleeve to align said centre with said axis, and fixing said rotary coded plate to said sleeve. The method preferably further includes a step of attaching a light sensor of said pulse encoder to said stationary coded plate. According to the above-mentioned method, the stationary coded plate can be centrally aligned by pushing same in one radial direction of the circular track pattern, and then the relative positioning of the rotary coded plate and the stationary coded plate can be accurately achieved by only the steps of, putting the clearance gauge on the stationary coded plate positioned by the central aligning; inserting the sleeve having the rotary coded plate attached thereon onto the output shaft; and fixing the sleeve to the shaft to cause the rotary coded plate to abut against the clearance gauge. Thus a motor having a highly accurate pulse encoder can be provided. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view showing the attachment of a stationary coded plate of the pulse encoder according to the method of the present invention; Figure 2 is a longitudinal local sectional view of Fig. 1 taken along the line II-II; Figure 3 is a longitudinal local sectional view showing one state of the working process whereby a rotary coded plate is attached on the basis of the stationary coded plate; and, Figure 4 is a plan view of a spring plate ring. BEST MODE FOR CARRYING OUT THE INVENTION Referring to Figs. 1 and 2, a C shaped annular portion 16 is integrated with a rear end 12 of a motor housing. An end surface 18 of the annular portion 16 has been ground at a right angle to a central axis 10 of an output shaft 14 of the motor holding the shaft 14. On the other hand, a plate 22 having light sensors is adhered on an annular coded plate 20 to be fixed so that the light sensors correspond to slits 36 of the fixed stationary coded plate 20. The stationary coded plate 20 having the light sensor plate 22 adhered thereon is placed on the end surface 18 of the C shaped annular portion 16 of the motor housing which is fixed to a work table (not shown) in a state such that a front end of the shaft 14 of the motor is directed downward. A triangular support plate 24 holding the other end of a half cylindrical member 26 provided with a threaded portion on the outer surface at least near one end of the member at one vertex portion thereof, is inserted through an open side of the C shaped annular portion 16 so that the half cylindrical member 26 surrounds the shaft 14. Then, the remaining two vertex portions are fixed to the rear end portion 12 of the motor housing by screw members 32. After the member 26 is thus immovably fixed, the stationary coded plate 20 is temporarily pushed onto the end surface 18 of the annular portion 16 and held by a nut 30. The motor housing is rotated around the fixed shaft 14 in a state such that the stationary coded plate 20 is temporarily fixed as above-mentioned, and a circular track 34 for a central alignment is drawn on the stationary coded plate 20 coaxially with the slits 36. It can be accurately seen from the above, by a microscope, that the circular track 34 during rotation projects most at a position crossing an imaginary radius line extending through a center of the circular track 34 from a point of the central axis 10, and retracts most at the opposite position when the stationary coded plate 20 temporarily fixed to the motor housing is rotated with the motor housing, if the center of the circular track 34 is not positioned on the central axis 10 of the shaft 14. Therefore, a central alignment is achieved only by pushing the stationary coded plate 20 having a circular outer periphery in the direction of the center deviation by the amount of deviation, calculated on the basis of the amounts of the projection and the retraction, by a jig tool (not shown). Then, the stationary coded plate 20 is precisely fixed on the end surface 18 of the annular portion 16 by coating an adhesive including an epoxy resin, etc., around the stationary coded plate 20. Then, the triangular support plate 24 having the half cylindrical member 26 is removed by removing the nut 30 and the screws 32. Next, referring to Fig. 3, the method for attaching a rotary coded plate on the basis of the stationary plate 20 will be explained hereinafter. A clearance gauge 50 having a prescribed thickness is placed upon the stationary plate 20. On the other hand, the rotary coded plate 48 is temporarily held by pressure from a spring plate ring 56 (refer to Fig. 4) operating to apply the spring force thereof onto a shoulder 46 of a sleeve 42, which shoulder has a high flatness. The sleeve 42 is provided with a hole 44 having a prescribed depth, to enable a press-fit insertion onto a smaller portion 40 of the rear end of the shaft 14 at one end thereof, and with a smaller portion 52 on the other end thereof to form the shoulder 46. The sleeve 42 temporarily holding the rotary coded plate 48 is inserted onto the smaller portion 40 of the shaft 14, the portion 40 being coated with an adhesive, until the rotary coded plate 48 abuts against the gauge 50, and left in this state until the adhesive is hardened. Then, the gauge 50 is removed, and the rotary coded plate 48 is centrally aligned in the same manner as the stationary coded plate 20. Namely, a circular track for a coaxial centering with each slit is also drawn on the rotary coded plate 48. This centering is achieved by fixing the motor housing and by observing through a microscope the trace of a circular track when the output shaft is rotated. The size of a central hole 54 of the rotary coded plate 48 is a little larger than the size of the smaller portion 52 of the sleeve 42, and is smaller than the size of the shoulder, so that the rotary coded plate 48 is placed on the shoulder 46 such that it can be moved in a radial direction by a jig tool when it is to be centrally aligned. After this centering is completed, an adhesive is filled therein from above the spring plate ring 56 to fix the rotary coded plate 48 to the sleeve 42. A hole 58 having a small diameter formed along an axis of the sleeve 42 allows air to be exhausted when the sleeve 42 is inserted onto the smaller portion 40 of the shaft 14. In this embodiment, the positioning of the light sensor plate 22 in alignment with the stationary coded plate 20 is easily effected because the former is directly fixed to the latter by an adhesive. Further, the positioning (centering) of the sleeve 42 in alignment with the rotary coded plate 48 can be achieved by a separate process because the fitting of the sleeve 42 and the smaller portion 40 of the shaft 14 can be accurately carried out. In such a case, the work efficiency for attaching the pulse encoder to the motor is further increased. The following is apparent from the foregoing description. The stationary coded plate is mounted accurately at a right angle to the central axis for rotation because the stationary coded plate is placed on the large end surface of the motor housing, which surface is machined at a right angle to the central axis of the shaft of the motor, and the centering can be achieved only by pushing the stationary coded plate in the specific radial direction of the circular track, because the circular track for centering is drawn on the stationary coded plate so that any central deviation of the circular track is observed during rotation of the motor housing. Namely, the centering can be achieved only by an adjustment thereof in a one-dimensional direction of the radius thereof. On the other hand, the clearance between the rotary coded plate and the stationary coded plate can be set only by abutting the rotary coded plate temporarily held on a sleeve against a prescribed gauge placed on the stationary coded plate mounted in the above-mentioned manner. The centering of the rotary coded plate also can be achieved only by an adjustment thereof in a one-dimensional direction of the radius using a circular track for centering. Accordingly, the pulse encoder can be built into the motor accurately and efficiently, and thus a motor having the pulse encoder with a high detection performance can be provided. LIST OF REFERENCE NUMERALS 10 Central axis of output shaft 12 Rear end of motor housing 14 Output shaft of motor 16 C shaped annular portion of motor housing 18 End surface of C shaped annular portion 20 stationary coded plate 22 Light sensor 24 Triangular support plate 26 Half cylindrical member 30 Nut 34 Circular track pattern for centering 36 Slits of stationary coded plate 42 Sleeve member 48 Rotary coded plate 50 Clearance gauge 56 Spring plate ring

Claims: A method of attaching a pulse encoder to a motor using a clearance gauge, characterised by: grinding a housing (16) of said motor to form a plane end surface (18) which is perpendicular to a rotation axis of an output shaft (14) of said motor; fixing a front end of said output shaft of said motor to a worktable in such a manner that a rear end of said output shaft of said motor is exposed within a portion of said housing (16) of said motor; fixing a stationary coded plate (20) of said pulse encoder to said housing plate end surface (18) by a process which includes: temporarily attaching said stationary coded plate (20) to said housing plane end surface (18) such that a circular track pattern (34) on said stationary coded plate surrounds said output shaft axis, rotating the housing (16) relative to said shaft to determine the deviation of the centre of the circular track Pattern (34) from said output shaft axis, moving said stationary coded plate (20) to align the centre of said circular track (34) with said output shaft axis, fixing said stationary coded plate (20) to said housing plane end surface (18), and attaching a rotary coded plate (48) of said pulse encoder to said output shaft rear end by a process which includes: mounting a sleeve (42), having said rotary coded plate (48) attached thereto, on said output shaft from said rear end with said clearance gauge (50) interposed between said stationary coded plate (20) and said rotary coded plate (48), advancing said sleeve on to said output shaft (40) until said rotary coded plate (48) abuts against said clearance gauge (50) in contact with said stationary coded plate (20), fixing said sleeve (42) to said output shaft, and removing said clearance gauge (50) after confirming the fixing of said output shaft to said sleeve. A method as claimed in claim 1, characterised in that said process for attaching said rotary coded plate further includes rotating said shaft relative to the housing to determine the deviation of a centre of a circular track pattern on said rotary coded plate from said output shaft axis, moving said rotary coded plate on said sleeve to align said centre with said axis, and fixing said rotary coded plate to said sleeve. A method as claimed in claim 1 or 2, characterised in that said method includes a further step of: attaching a light sensor of said pulse encoder to said stationary coded plate.

Inventors: USHIYAMA, SHIGEYUKI, YAMAMOTO, TOMONAGA
Applicants: FANUC LTD.
Application year: 1987
Main classification: G01D5
IPC codes: H02K11, G01D5