ROTARY OPTICAL TRANSDUCER

Abstract: The optical transducer is connected to a rotary shaft (71) for detecting the angular position thereof and generates cor­ responding electrical signals. The transducer comprises a cas­ ing formed by two casing halves (11, 12) which can be as­ sembled together by means of latch elements (62, 63). Mounted on a first casing half (11) are three phototransistors (31, 32) for detecting the light emitted by a diode (58) mounted on the other casing half (12). A shutter disc (64) which is pro­ vided with radial openings is mounted rotatably within the cas­ ing on the shaft (71) which is supported by a self-aligning bush (19) which is mounted on a casing half. A flexible printed circuit (38) is disposed within the first casing half, parallel to the shut­ ter disc and is in contact with the three phototransistors. The printed circuit has a projecting portion (43) which is bent over inside the casing so as to contact the diode (58) and a project­ ing portion (39) which extends out of the casing to be con­ nected to an external connector. In another embodiment the second casing half also has a self-aligning bush for the shaft.

Description: The present invention relates to an optical transducer for detecting different angular positions of a rotary member with respect to a fixed structure, comprising a light emitter for emitting a light beam, at least one light detector a casing formed by first and second casing halves and in which are mounted the light emitter and the light detector, a shutter disc lodged in the said casing and connectable to the rotary member for rotation around a given axis, bush means carried by the first casing half for defining an axis of rotation for the shutter disc, and disc mounting means for positioning axially the shutter disc with respect to the bush means, the light emitter and the light detector, wherein the first casing half is connectable to the fixed structure and the shutter disc has a plurality of transparent radial elements alternated with opaque radial elements and crossed by the light beam for casing the light detector to generate electrical signals indicative of the different angular positions of the rotary member. Such a transducer is known from EP-A-0003153. A transducer is known, wherein the shutter disc is provided with a central hub. The disc and hub are housed with clearance within two casing halves and, for precisely positioning the transducer with respect to the rotary member and in particular the shutter disc with respect to the light emitting and detecting elements, the arrangement has three separate positioning elements. A first element comprising an axial abutment which is fixed to the rotary member co-operates with the shutter disc to position it axially with respect to the rotary member; a second element which is provided directly on an outside wall of the casing axially positions same with respect to the rotary member; and a third element which is formed by a removable bush is used for radially positioning the casing with respect to the rotary member. While this known transducer has been found to be highly accurate and thus suitable for detecting even very small angular movements of the rotary member, it is fairly expensive both in regard to construction and assembly. EP-A-006002l discloses an optical transducer of the general type described. However, this transducer does not provide any bush means to define the axis of rotation of the shutter disc. The object of the present invention is to provide an optical transducer which is very simple in design and wherein the connection thereof to the rotary member is a simple operation and such as not to require the use of particular positioning elements. The invention is characterised in that the bush comprises a self-aligning bush member having a spherical outer surface and a seat of the first casing half having an inner surface cooperative with the spherical outer surface of the bush member to enable the inclination of the axis of rotation of the shutter disc with respect of the first casing half to be adjusted. The invention will be described in more detail by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of a transducer according to the invention, in a first embodiment, Figure 2 is a front view of a first casing half of the transducer shown in Figure 1, Figure 3 is a front view of a second casing half of the transducer shown in Figure 1, and Figure 4 is a sectional side view of a transducer according to the invention in a second embodiment. Referring to Figure 1, an optical transducer 10 comprises a casing formed by a first casing half 11 and a second casing half 12 which are snapped together and which are made of opaque plastics material, such as for example a polycarbonate. The casing half 11 is of such a configuration as to have a substantially square front wall 13 (see Figures 1 and 2), from which projects a substantially cylindrical wall 14 which defines an internal cavity 16. Provided in a central region 17 of the front wall 13 is a seat 18 for a self-aligning bush 19 of known type, having a central hole 21 passing therethrough and a spherical outside surface 22. The central region 17 is externally provided with a reference surface 23. The casing half 11, inside the cavity 16, is provided with a support 24 carrying three cylindrical seats 26, 27 and 28 where three corresponding phototransistors 29, 31 and 32 are housed. Fixed in front of the three phototransistors 29, 31 and 32 is a light collimation mask 33 comprising for example a metal plate having photo-engraved openings 34. The mask 33 is substantially parallel to the external reference surface 23. Provided on the wall 13, in line with the three phototransistors 29, 31 and 32 is an aperture 36 which can be closed by a rubber plug 37. A printed circuit 38 is also arranged within the cavity 16 in the casing half 11, and comprises a disc-shaped sheet of flexible plastics material of a thickness of a few tenths of a millimetre. The printed circuit 38 is connected to the phototransistors 29, 31 and 32 and is provided with a first, upper tongue 39 which is arranged to extend out of the casing 11 through an opening 41 to be connected to an external connector 42, and a second tongue 43 which is arranged to be inserted within the casing half 12. Three posts 44 which are disposed within the cavity 16 support and position the printed circuit 38 with respect to the casing half 11. Circuit components 46 of known type are mounted on the circuit 38. The second casing half 12 (see Figures 1 and 3) is of such a configuration as to provide a front wall 51 and a side wall 52 which define a substantially cylindrical cavity 53. The wall 51 is provided with a central hole 54, which can be closed by means of a plug-in cap 56 of substantially cylindrical shape and made of plastics or rubber. Provided on the wall 51 is a seat 57 within which is disposed a light emitting diode (LED) 58. Arranged in front of the LED 58 and supported by two projecting portions 59 is a light diffusing elements 61 formed for example by a plate of transparent plastics material. The diffuser 61 is substantially parallel to the mask 33, when the two casing halves 11 and 12 are fitted together, and provides that the beam of light emitted by the LED 58 is substantially perpendicular to the mask 33. The casing half 12 is provided with a pair of ribs 62 which are disposed within the side wall 52 and which are arranged to snap into latching engagement with corresponding grooves 63 which are provided on the cylindrical portion 14 of the casing half 11, thus to form the connection between the two casing halves 11 and 12. The transducer 10 further comprises a shutter disc 64 which may be of metal or opaque plastics material, and is provided with a plurality of radial openings which are disposed on a circular ring coaxial with a central hole 67 and disposed in alignment with the phototransistors 29 and 31. A single opening 68 is provided in the disc 64 at a more inward location with respect to the openings 66, thereby to co-operate with the phototransistor 32. The radial openings 66 are angularly equally spaced from each other and the number thereof may vary between 100 and 500, depending on the type of use for which the transducer is intended. The openings 66 thus define transparent regions which are spaced by opaque regions. The transducer 10 as described hereinbefore can be connected to a rotary member for detecting the angular position thereof and generating corresponding electrical signals. By way of indication, in Figure 1, the transducer 10 is shown coupled to a cylindrical shaft 71 of an electric motor 72. The shaft 71 is of the same diameter as the hole 21 in the bush 19 and the hole 67 in the shutter disc 64. The casing half 11 is arranged to be fixed to the body of the motor 72, for example by means of screws (not shown) which can be fitted into holes 73 in the wall 13, in such a way that the front surface 23 is held against a corresponding reference wall portion 74 of the motor 72, which is orthogonal to the axis of rotation of the shaft 71. A cylindrical spacer 76 is fitted coaxially to the shaft 71 to hold the shutter disc 64 at a predetermined axial spacing from the bush 19. A cylindrical sleeve 77 is fitted coaxially to the shaft 71 for locking the disc 64 with respect to the shaft 71, by means of a grub screw 78. The operation of mounting the transducer 10 and connecting it to the shaft 71 are carried out in the following manner: The two casing halves 11 and 12 are first prepared separately, with the casing half 11 accommodating the bush 19, the three phototransistors 29, 31 and 32, the mask 33 and the printed circuit 38, and the casing half 12 accommodating the LED 58 and the light diffuser 61. The conductor wires of the phototransistors 29, 31 and 32 are soldered to the printed circuit 38 through the opening 36 in the wall 13 of the casing half 11, whereupon the opening 36 is closed by means of the plug 37 to prevent light and impurities from entering the interior of the transducer. When the casing half 11 has been prepared in that way, it is fitted on to the shaft 71. More particularly, the shaft 71 is precisely inserted into the hole 21 in the bush 19 which is self-adjusting in its seat 18. When the reference surface 23 of the casing half 11 is brought into contact with the wall 74 of the motor 72, the shaft 71 is disposed perpendicularly to the mask 33. The casing half 11 is thus fixed to the motor 72. The spacer 76, the shutter disc 64 and the sleeve 77 are then fitted onto the shaft 7l, and the arrangement is locked by means of the grub screw 78. In that way, the disc 64 is axially positioned with respect to the mask 33 and is parallel thereto. Finally, the casing half 12 is fitted to the casing half 11 by means of the teeth 62 which are in latching engagement with the recesses 63. The projection portion 43 on the printed circuit 38 is then connected, for example by means of soldering, to the conductors of the LED 58. The shutter disc 64 is thus parallel to the light diffuser 61 and therefore perpendicular to the beam of light emitted by the LED 58. The central hole 54 in the casing half 12 is closed by the cap 56 to prevent light and impurities from entering the interior of the transducer. Before the two casing halves 11 and 12 are locked together, a check is carried out in regard to their mutual angular positioning. In accordance with a feature of the invention, that check is performed by detecting by means of an oscilloscope the two analog signals generated in response to the light detected by the photodetectors 29 and 31, and by rotating the casing half 12 with respect to the casing half 11 in the clockwise or anticlockwise direction, until the two analog signals are equal in amplitude, that is to say, until the LED 58 is correctly positioned with respect to the two corresponding phototransistors 29 and 31. That relative rotary movement as between the two casing halves 11 and l2 is possible because the length of the grooves 63 is greater than the length of the corresponding ribs 62. When this checking operation has been carried out, the two casing halves 11 and 12 are locked together in any known fashion, for example by means of an adhesive. The mode of operation of the transducer 10 as described hereinbefore is conventional and will not be described herein for the sake of brevity. In accordance with the second embodiment, shown in Figure 4, an optical transducer 100 comprises a casing formed by two casing halves 111 and 112 which are capable of supporting a cylindrical shaft 120 by means of two self-aligning bushes 113 and 114 which are housed in seats 115 and 116 respectively. The cylindrical shaft 120 has an end portion 121 which projects out of the casing of the transducer to be connected in any known manner, for example by means of an elastic coupling joint, to the rotary member whose angular position is to be detected. The casing half 112 is identical to the casing half 12 and carries the same light detector and circuit elements as those used in the transducer of Fig 1, so that the description thereof will now be repeated here. As regards the optical portion, the casing half 111 is largely the same as the above-described casing half 11. A shutter disc 130 is free to rotate within the two casing halves, the shutter disc 130 being identical to the disc 64 and being mounted on the shaft 120 between the bushes 113 and 114 by means of a cylindrical spacer 131 and cup springs 132. The disc 130 is locked on the shaft 120 in any known manner during the operation of assembling the transducer. It will be clearly apparent from the foregoing description that at least one self-aligning bush l9, 113 is mounted on one of the two casing halves 11, 111 of the transducer 10, 100, and that the bush co-operates with the rotary member 71, 120 to hold the shutter disc 64, 130 orthogonal with respect to the beam of light emitted by the light emitter 58.

Claims: An optical transducer (10,100) for detecting different angular positions of a rotary member with respect to a fixed structure, comprising a light emitter (58) for emitting a light beam, at least one light detector (29, 31, 32), a casing formed by first and second casing halves (11, 12; 111, 112) and in which are mounted the light emitter and the light detector, a shutter disc (64; 130) lodged in the said casing for rotation around a given axis, bush carried by the first casing half for defining an axis of rotation for the shutter disc, and disc mounting means (76, 77, 78; 131, 132) for locking the shutter disk to the rotating member and positioning axially the shutter disc with respect to the bush means, the light emitter and the light detector, wherein the first casing half (11; 111) comprises means (73) for fixing the transducer to the fined structure and the shutter disc has a plurality of transparent radial elements alternated with opaque radial elements and crossed by the light been for causing the light detector to generate electrical signals indicative of the different angular positions of the rotary member, characterised in that the bush comprises a self-aligning bush member (19; 113) having a spherical outer surface (22) and a seat (18; 115) of toe first casing half (11; 111) having an inner surface cooperative with the spherical outer surface of the bush member to enable the inclination of the axis of rotation of the shutter disc with respect to the first casing half to be adjusted. A transducer (10) according to claim 1, characterised in that the first casing half (11) is provided with flange means to be fixed to a reference wall (74) of the fixed structure (72), wherein the said rotary member (71) comprises a cylindrical shaft projecting from the reference wall and a central hole (21) of the bush member cooperative with the said cylindrical shaft for rotational and axial movement thereof with respect to the casing halves, and wherein the disc mounting means (76, 77, 78) are provided to fix the shutter disc (64) removably on the cylindrical shaft for rotation thereby. A transducer according to clad 2, characterised in that the disc mounting means comprise a spacer membe r (76) and a sleeve member (77) fitted coaaxially with the cylindrical shaft at opposite faces of the shutter disc (64); and a grub screw (78) carried by the sleeve member and locked onto the cylindrical shaft to axially and radially lock the shutter disc on the cylindrical shaft at a predetermined axial position with respect to the bush member (19). An optical transducer according to claim 3, characterised in that the second casing half (12) comprises a central hole (54) and wherein a plug-in cap (56) closes the central hole to prevent light and impurities from entering the interior of the transducer. A transducer (100) according to claim 1, characterised by a further self-aligning member (114) having a spherical outer surface (116); a seat (116) in the second casing half (112) cooperative with the spherical outer surface of the said further self-aligning bush member; and a supporting shaft (121) rotatably supported by the self-aligning bush members (113, 114) and supporting the shutter disc (114); wherein the disc mounting means (131, 132) couple fixedly the shutter disc with the support shaft (120) and wherein the support shaft projects frcm the one bush meeber (113) out of the first casing half (37) for connection with the rotatable member. A transducer according to claim 5, characterised in that the disc mounting means comprises a cup spring (132) bearing on the other bush member (114) and urging the shutter disc (130) towards a given arrest position. A transducer according to claim 5 or 6, characterised by a spacer member (131) interposed between the shutter disc (130) and the one bush member (113) and cooperative with the one bush member and the shutter disc to hold the said shutter disc at a feed axial position defined by the one bush member. An optical transducer according to any of the preceding claims, characterised in that, disposed within the casing (11, 12), is a f1eiible printed circuit (38) connected to the light detector (29, 31, 32) and the light emitter (58) and having a projecting portion (39) which extends out of the casing halves to be connected to an external connector. A transducer according to claim 8, characterised in that the printed circuit comprises a first portion (39) mounted on the first casing half (11, 111) adjacent the disc (64, 130) and supporting electrical components (46) and LEDs of one (31, 32) of the light emitter (58) and light detector (31, 32) and a second portion (43) encompassing the shutter disc (64, 130) to connect the LEDs of the other (58) of the light emitter (58) and light detector (31, 32). An optical transducer according to any of the preceding claims, characterised in that the casing halves (11, 12; 11, 112) are held together by ribs (62) on one of the casing halves (12) and recesses (63) on the other of the casing halves (11), the ribs and recesses permitting relative rotational movement as between the one and the other casing halves after coupling thereof to modify the relative position as between the light detector (31, 32) and the light emitter (58). An optical transducer accroding to claim 10, characterised in that the ribs and recesses comprise a circular rib portion (62) on one of the casing halves and a complementary recess on the other casing half. A transducer according to claim 11, wherein the rib portion is provided on the inside of a peripheral wall of one of the casing halves (12) and the complementary recess (63) is provided on the outside of the peripheral wall (14) of the other casing halves.

Inventors: CALIGARIS CAPPIO, EMILIO, GUERRINI, GIAMPAOLO
Applicants: ING. C. OLIVETTI & C., S.P.A.
Application year: 1984
Main classification: G01D5
IPC codes: G01D5