Abstract:
A rotation detector has a simple structure and operates reliably to check quickly for erroneous installation as an encoder for detecting the rotation rate of a multi-rotation body that rotates for a finite number of revolutions of one revolution or more. A stator member is formed of a housing and a cover coupled together, and a detection window is formed on an outer peripheral wall of the housing. A rotor member is rotatably supported by the housing and the cover, and a rotary ring arranged concentrically with the center of rotation of the rotor member is housed in the stator member. Rotation of the rotor member is intermittently transmitted to the rotary ring via an intermediate gear. According to the variation of outputs from photointerrupters that turn on or off according to the rotation of the rotary ring, an absolute position of the rotor member is detected. Also, an indicator is arranged on the rotary ring so that the indicator is visible through the detection window  1   b  only when the rotary ring is in a neutral position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotation detector for a multi-rotation body which rotates for a finite number of revolutions of one revolution or more, and particularly, to a rotation detector suitable for detecting an absolute position of the multi-rotation body. 
     2. Description of the Related Art 
     Conventionally, there is proposed a rotation detector, as described in Japanese Examined Utility Model Publication No. 5-26487, using an increment-type encoder to detect a precise rotation angle within one revolution of a steering wheel. It also uses an absolute-type encoder to detect a rough rotation angle of more than one revolution of the steering wheel. The detector then combines the precise rotation angle and the rough angle to determine the rotation angle from a neutral position of the steering wheel 
     The increment-type encoder is composed mainly of a code plate that rotates integrally with a steering shaft and photointerrupters opposing each other via the code plate. This encoder can detect only rotation angles of the code plate within one revolution. However, since the code plate rotates integrally with the steering shaft, the detection accuracy is high. 
     The absolute-type encoder is composed mainly of a substrate on which a resistance pattern is formed, a reduced-speed rotating body having a brush that slidably contacts the resistance pattern, and a gear mechanism for transmitting rotation of the steering wheel to the reduced-speed rotating body. In this case, since the rotation of the steering wheel that rotates multiple times is reduced to rotation within one cycle of the reduced-speed rotating body via the gear mechanism, an absolute position of the steering wheel can be detected. 
     In installation of the rotation detector as described above in a steering unit of a motor vehicle, however, the reduced-speed rotating body of the absolute-type encoder must be set to a neutral state in the rotation direction. If the reduced-speed rotating body is erroneously installed in a state which deviates from the neutral point, a precise absolute position of the steering wheel cannot be detected. 
     For this reason, in the conventional example as described above, after the installation of the absolute-type encoder in the steering unit, resistances which vary depending upon the position where the resistance pattern and the brush slidably contact must be electrically measured. Then, according to the variation in the resistance, a rotation status of the reduced-speed rotating body must be checked. This causes a reduction in efficiency of the installation of the rotation detector. 
     Also, in the conventional example, the gear mechanism composed of a sun gear arranged on a rotor member, a ring-like gear arranged on a stator member, and a planet gear engaged between the sun gear and the ring-like gear is used as the absolute-type encoder. Therefore, the arrangement space of the gear mechanism occupies in the whole rotation detector is relatively large. This causes a problem in that miniaturization of the rotation detector is difficult. 
     Furthermore, since the planet gear always engages with both the sun gear and the ring-like gear, the reduced-speed rotating body supporting the planet gear is rotated even by a minute rotation of the steering wheel. Particularly, since the rotation (operation) rate is subsequently high in the vicinity of the neutral position, a problem is caused in that the resistance pattern is locally worn away. 
     SUMMARY OF THE PRESENT INVENTION 
     An object of the present invention is, therefore, to provide a rotation detector having a simple structure, operating reliably, and having a capacity of checking quickly for erroneous installation as an encoder for detecting the rotation rate of a multi-rotation body that rotates for a finite number of revolutions of one revolution or more. 
     To achieve this object and other objects described herein, according to the present invention, a rotation detector for a multi-rotation body, as described below is provided. 
     The rotation detector for a multi-rotation body has a rotor member integrally rotating with a code plate of a rotary encoder, a rotary member arranged concentrically with the center of rotation of the rotor member, an intermediate gear for intermittently transmitting rotation of the rotor member to the rotary member, detecting elements for detecting an amount of rotation of the rotary member, and a stator member enclosing the rotary member, the intermediate gear, and the detecting elements. 
     In the rotation detector for a multi-rotation body the stator member has a detection window through which an indicator for indicating a neutral rotation position of the rotary member can be viewed. 
     In this arrangement, the intermediate gear may be supported by the stator member, and the indicator is arranged on the rotary member. Also, the intermediate gear may be supported by the rotary member, and the indicator may be arranged on at least one of the intermediate gear and the rotary member. 
     As described above, the intermediate gear may be supported either by the stator member or by the rotary member. In the case of the intermediate gear being supported by the stator member, however, the indicator must be arranged with the stator member. In the case of the intermediate gear being supported by the rotary member, the indicator may be arranged on at least one of the intermediate gear and the rotary member. 
     Furthermore, the detection window may be arranged on an outer peripheral wall of the stator member. Furthermore, the detection window may be arranged on a cover of the stator member. 
     In the present invention as described above, rotation of the rotor member is transmitted intermittently to the rotary member via the intermediate gear, and the amount of rotation of the rotary member is detected by means of the detecting elements such as photointerrupters. Concurrently, the detection window is arranged on the stator member that encloses the rotary member and the detecting elements to allow an indicator of the rotary member to be viewed. 
     According to the present invention configured as described above, a neutral rotation position of the rotary member can be visually checked, improving efficiency of installation of the rotation detector. Also, the intermediate gear intermittently transmits rotation of the rotor member to the rotary member. This provides an advantage in that the amount of local abrasion in structural components due to continuous operation can be significantly reduced. 
     Furthermore, the need for excessive large layout spaces for the individual structural components can be avoided. Therefore, miniaturization of the rotation detector for the multi-rotation body can be achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a bottom plan view of a rotation detector according to an embodiment of the present invention; 
     FIG. 2 is a side view of the rotation detector; 
     FIG. 3 is a cross-sectional view of the rotation detector; 
     FIG. 4 is a bottom plan view of the rotation detector without a cover; 
     FIG. 5 is a bottom plan view of the rotation detector without the cover and a code plate; 
     FIG. 6 is a perspective view showing main portions of a gear mechanism in the rotation detector; 
     FIG. 7 is illustrative of operation of the gear mechanism. 
     FIG. 8 is a bottom plan view of a rotation detector according to another embodiment of the present invention; and 
     FIG. 9 is a bottom plan view of main portions of a rotation detector according to another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments are described below with reference to the drawings. 
     FIG. 1 is a bottom plan view of a rotation detector according to the embodiment. FIG. 2 is a side view of the rotation detector. FIG. 3 is a cross-sectional view of the rotation detector. FIG. 4 is a bottom plan view of the rotation detector without a cover. FIG. 5 is a bottom plan view of the rotation detector without the cover and a code. FIG. 6 is a perspective view of main portions of a gear mechanism arranged in the rotation detector. FIG. 7 is a drawing for explanation of operation of the gear mechanism. 
     The rotation detector of the embodiment has a housing  1  that includes a guide opening  1   a  on a top surface, a cover  3  that includes a guide opening  3   a  and which covers a lower opening of the housing  1 , and a rotor member  2  that is rotatable around the center of the guide openings  1   a  and  3   a . The housing  1  and the cover  3  house an increment-type encoder and an absolute-type encoder for rotation-rate verification, which are described below. A detection window  1   b  is formed on an outer peripheral wall of the housing  1 , and the cover  3  is integrally coupled with the housing  1  in a manner such as snap-coupling. The housing  1  and the cover  3  constitute a stator member, and are fixed by screws, for example, with a casing of a combination switch and an immobilizing body of a rotation connector when the rotation detector is assembled in a steering unit of a motor vehicle. 
     As shown in FIG. 3, the rotor member  2  is composed of a first rotor  4  and a second rotor  5 , and the two rotors  4  and  5  are integrally coupled by a plurality of screws  7  via a code plate  6 . A center opening  8  is formed through the two rotors  4  and  5  and the code plate  6 . In installation of the rotation detector in a steering unit of a motor vehicle, a steering shaft (not shown) is inserted through the center opening  8 , and the steering shaft rotates together with the two rotors  4  and  5  and the code plate  6 . 
     As shown in FIG. 4, a plurality of throughholes  6   a  are formed on the code plate  6  along the peripheral direction thereof. A-phase and B-phase patterns are detected by three photointerrupters  9  arranged in such a manner as to cross the throughholes  6   a . The code plate  6  and the individual photointerrupters  9  constitute the increment-type encoder, and the increment-type encoder detects, with high accuracy, rotation angles of the code plate  6  within one revolution. 
     The absolute-type encoder is described below. 
     As shown in FIG. 5, a rotary ring  10  is arranged as a rotary member in the housing  1 . The rotary ring  10  is rotatable on a locus sharing the same center with the guide opening  1   a . A driven gear  11  is engraved on the rotary ring  10  over a range of substantially 90 degrees. An indicator  12  is arranged on an outer peripheral surface of the driven gear  11  for indicating a neutral rotation position of the rotary ring  10 . The indicator  12  may be any type as long as it is viewable through the detection window  1   b  of the housing  1  during rotation of the rotary ring  10 . For example, it may be of the type of a printed marking on the outer peripheral surface of the driven gear  11 , and it may be integrally formed with the rotary ring  10 . 
     On the rotary ring  10  is also arranged a light shield  10   a  in such a manner as to oppose the driven gear  11  through the center opening  8 . Arranged also thereon are four photointerrupters  13   a  to  13   d  mounted on a printed board (not shown) in a manner such as to cross the light shield  10   a.    
     An intermediate gear  14  engages with the driven gear  11 . The intermediate gear  14  is rotatably supported by a boss  1   c  erected on an upper internal surface of the housing  1  and is dislodged by a screw  15 . As shown in FIGS. 3 and 5, the intermediate gear  14  has a first toothed section  14   a  consisting of four teeth arranged at every 90 degrees. Similarly arranged is a second toothed section  14   b  consisting of four teeth arranged at every 90 degrees, with a relative phase difference of 45 degrees to the first toothed section  14   a . The first and second toothed sections  14   a  and  14   b  are positioned in such a manner as to deviate from each other in the axial direction. 
     FIG. 6 is an inverted perspective view of the rotation detector. As shown in the figure, a small-diameter section  4   a  and a large-diameter section  4   b  are formed on an outer peripheral surface with a lateral step therebetween. The small-diameter section  4   a  opposes the first toothed section  14   a  of the intermediate gear  14 , and the large-diameter section  4   b  opposes the second toothed section  14   b . A relief groove  16  is formed on the large-diameter section  4   b , and at two sides of the relief groove  16  are formed engaging-projection sections  17   a  and  17   b.    
     As shown in FIG. 7A, when a first rotor  4  rotates in the direction of arrow A (counterclockwise direction), one tooth of the first toothed section  14   a  opposing the small-diameter section  4   a  contacts the engaging-projection section  17   a . Therefore, as shown in FIG. 7B, the intermediate gear  14  rotates by substantially 45 degrees in the direction of arrow B, and one of the second toothed section  14   b  engages with the relief groove  16 . 
     When the first rotor  4  further rotates from the above state in the direction of arrow A, one tooth second toothed section  14   b  being engaged with the relief groove  16  is pushed by the other engaging-projection section  17   a . Then, the intermediate gear  14  further rotates by substantially 45 degrees in the direction of arrow B, and next, one tooth of the first toothed section  14   a  opposes again the small-diameter section  4   a . Specifically, the intermediate gear  14  rotates by substantially 90 degrees until the state in FIG. 7A changes to the state in FIG.  7 C. Therefore, the driven gear  11  is fed by two teeth in the direction of arrow C, and the rotary ring  10  rotates in the direction of arrow C by a determined amount of rotation. Consecutively, when the engaging-projection section  17   a  passes the intermediate gear  14 , two teeth of the second toothed section  14   b  oppose the large-diameter section  4   b  during the subsequent rotation of the first rotor  4 . Therefore, non-engaging rotation of the intermediate gear  14  can be avoided. 
     In this way, during one revolution of the first rotor  4 , the intermediate gear  14  is rotated by substantially 90 degrees by the engaging-projection sections  17   a  and  17   b . Therefore, the light shield  10   a  also rotates by two teeth in the same direction and moves to a position where an adjacent photointerrupter emits light. That is, since the photointerrupters  13   a  to  13   d  that are switched on produces variable outputs, an absolute position (amount of rotation) of the first rotor  4  can thereby be detected. 
     In installation of the rotation detector configured in the above manner in a steering unit of a motor vehicle, the rotary ring  10  which is a component of the absolute-type encoder must be set at a neutral position. In this case, as shown in FIG. 2, when the indicator  12  is visible from the outside of the housing  1  through the detection window  1   b , the rotary ring  10  can be determined to have been set to the neutral position. On the contrary, if the indicator  12  is invisible through the detection window  1   b , the rotary ring  10  can be determined to have been set to a position deviated from the neutral position. In this case, the position of the rotary ring  10  must be adjusted to the neutral position by rotating the rotor member  2 . 
     In this way, since the neutral position of the rotary ring  10  can be visually checked, efficiency in the installation of the rotation detector in the steering unit can be improved. Particularly, this embodiment has the detection window  1   b  formed on the outer peripheral wall of the housing  1 . Therefore, even after the rotation detector is mounted between a combination switch and a rotation connector or a steering wheel (which are not shown), existence of the indicator  12  can be confirmed from a lateral side thereof on the outside. 
     When the rotation detector is installed in the steering unit as described above, the rotor member  2  of the rotation detector rotates together with a steering shaft (not shown). Hereinbelow, a description regarding operation regarding the rotation detector is given. For instance, as shown in FIG. 5, when the photointerrupter  13   c  is shielded by the light shield  10   a , only the photointerrupter  13   c  turns on, and the other photointerrupters  13   a ,  13   b , and  13   d  turn off. In this case, the steering wheel is detected to be within a range of o to 360 degrees with respect to the center reference thereof. On the other hand, the rotation angle of the steering wheel within a range of 0 to 360 degrees is detected with high accuracy by the individual photointerrupters  9  of the increment-type encoder. 
     When the rotor member  2  (the first rotor  4 ) rotates counterclockwise from the state shown in FIG. 5, and the light shield  10   a  shields both the photointerrupter  13   c  and the adjacent photointerrupter  13   d , these photointerrupters  13   c  and  13   d  turn on. Thereby, the steering wheel is detected to be in the position of 360 degrees. When the rotor member  2  further rotates counterclockwise, and only the photointerrupter  13   d  turns on, the steering wheel is detected to be within a range of 360 to 720 degrees. Concurrently, the rotation angle of the steering wheel within the above detected range is detected with high accuracy by the increment-type encoder. In a manner similar to the above, according to combinations of on/off operations of the individual photointerrupters  13   a  to  13   d , the steering wheel is detected to be within a range of −720 to +720 degrees. 
     The above embodiment is described in a case in which the detection window  1   b  is formed on the outer peripheral wall of the housing  1 . The arrangement location of the detection window  1   b  is, however, not limited to the outer peripheral wall. As a detection window  3   b  in FIG. 8, the detection window may be formed on a cover  3  so that an indicator  12  arranged inside can be viewed through the detection window  3   b . That is, the detection window may be arranged at an appropriate location as required as long as it is a member constituting the stator member. 
     For reference, a colorless or colored transparent cover may be used to cover the detection windows  1   b  and  3   b  for improvement in dust-proofness. 
     The above embodiment is also described in a case in which the driven gear  11  is arranged on the rotary ring  10 , and the intermediate gear  14  that engages with the driven gear  11  is supported by the housing  1 . As in an embodiment shown in FIG. 9, however, a driven gear  11  may be arranged on a housing  1  on an immobilized side so as not to rotate. In addition, an intermediate gear  14  may be arranged on a rotary ring  10 . 
     In this case, an indicator  12  is arranged on the intermediate gear  14  supported by the rotary ring  10 . Also, a detection window through which the indicator  12  can be viewed is arranged on a cover (not shown). The position of the indicator  12  is, however, not limited to the intermediate gear  14 , and it may instead be arranged on the rotary ring  10 . 
     In the embodiment shown in FIG. 9, during one revolution of a first rotor  4 , when the intermediate gear  14  is rotated by engaging-projection sections  17   a  and  17   b , the intermediate gear  14  rotates by substantially 90 degrees and also rotates around a first rotor  4 . Therefore, the rotary ring  10  which supports the intermediate gear  14  rotates by two teeth of the driven gear  11 . Accordingly, a light shield  10   a  arranged on the rotary ring  10  also rotates by two teeth, moving to the position where the adjacent photointerrupter shields light. That is, since outputs of the turned-on photointerrupters  13   a  to  13   d  vary, an absolute position (amount of rotation) of the first rotor  4  is thereby detected.