Abstract:
A multi-beam photoelectric sensor is disclosed which can be fabricated by selecting the length of a light projection/light-receiving columnar member and the number and pitches of optical axes in accordance with the width of a hazardous area of an object or the diameter of the minimum object to be detected. A projector string or a photo-detector string includes an optical module string having an alignment of a plurality of optical modules with an optical system for one optical axis, a light projection circuit for one optical axis and a plurality of flip-flops corresponding to one stage of a shift register, integrated with each other, and a flat cable. The flip-flops in the adjacent optical modules are connected in cascade by the adjacent module conduction wires thereby to make up a shift register. The optical modules making the optical module string are sequentially activated by the data sequentially sent by the shift register.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a multi-beam photoelectric sensor used for monitoring a person intruding into a hazardous area, or in particular to a multi-beam photoelectric sensor in which the length of the light projection and receiving columnar members, the number and the pitches of the optical axes can be changed in versatile fashion in accordance with the width of the hazardous area to be monitored or the minimum diameter of an object detected. 
   2. Description of the Related Art 
   The multi-beam photoelectric sensor of this type, as well known, comprises at least a light projection columnar member having a columnar case for accommodating a light projection string and at least a light-receiving columnar member having a columnar case for accommodating a photo-detector string, wherein the light projection and light-receiving columnar members are arranged with the light projection and light-receiving surfaces thereof in appropriately spaced and opposed relation to each other thereby to form an object-detecting light curtain between the light projection and light-receiving columnar members. 
   In the prior art, the light projector string and the photo-detector string accommodated in the columnar case is generally configured of a combination of the multi-beam optical modules having a unit number of optical axes (say, 4, 8 or 16 optical axes). In this multi-beam optical module, as many optical elements as the unit number of the optical axes (the light-emitting elements and the light projection lenses for the light projector, and the light-receiving elements and the light-receiving lenses for the photo-detector) are held integrally by a resin holder having a fixed pitch of optical axes. 
   In this conventional multi-beam photoelectric sensor, however, the length of the light projection and light-receiving columnar members and the number and the pitches of the optical axes are determined by a combination of the multi-beam optical modules having the fixed number and the fixed pitches of optical axes. It is therefore not easy to change the length of the light projection/light-receiving columnar member or the number and the pitches of optical axes in versatile way in accordance with the width of the hazardous area or the minimum diameter of the object to be detected. 
   In view of this, the present applicant has earlier proposed a novel multi-beam photoelectric sensor in which the light projector string and the photo-detector string accommodated in the columnar case are configured of a mass of single-beam optical modules (see Japanese Unexamined Patent Publication No. 2002-124170). 
   This novel multi-beam photoelectric sensor, in which the light projector string and the photo-detector string accommodated in the columnar case are configured of a mass of single-beam optical modules, can be fabricated by selecting the length of the light projection/light-receiving columnar member for each unit of optical axis. Thus, a light curtain most suitable for the width of a hazardous area to be monitored can be advantageously generated. 
   In the aforementioned multi-beam photoelectric sensor proposed earlier by the present applicant, the optical parts making up the projection optical system or the light-receiving optical system are accommodated in each module, and as compared with the other conventional light curtains, a light curtain having the number of optical axes most suitable for the width of the hazardous area to be monitored can be easily generated. With regard to the electrical parts such as the light projection circuit and the light-receiving circuit corresponding to each module, however, the circuit boards corresponding to a plurality of different optical modules are prepared and combined to meet the requirement of an arbitrary number of optical modules. Thus, it is necessary to hold a plurality of types of circuit boards in stock. As far as the circuit boards are concerned, therefore, the number of the parts of the circuit board in stock cannot be reduced to less than a predetermined amount. 
   SUMMARY OF THE INVENTION 
   The object of this invention is to provide a multi-beam photoelectric sensor in which the same electrical parts used for each optical axis are modularized for each optical axis, thereby making it possible to reduce the number of types of circuit boards prepared to generate the light curtain of the number of optical axes most suitable to the width of a hazardous area to be monitored. 
   The above and other objects, features and advantages of the invention will be easily understood by those skilled in the art by referring to the following description of the specification. 
   According to this invention, there is provided a multi-beam photoelectric sensor comprising at least a light projection columnar member including a columnar case for accommodating a light projector string and at least a light-receiving columnar member having a columnar case for accommodating a photo-detector string, wherein the light projection columnar member and the light-receiving columnar member are arranged with the light projection surfaces and the light receiving surfaces thereof in appropriately spaced relationship with each other thereby to generate a light curtain between the light projection columnar member and the light-receiving columnar member for detecting an object. 
   This multi-beam photoelectric sensor comprises a light projector string constituting a light projection module string including a plurality of aligned light projection modules having an integration of a light projection optical system for one optical axis, a light projection circuit for one optical axis and flip-flops corresponding to one stage of shift register, and an optical signal transmission member including a common conduction wire for uniformly connecting from a light projection module located at an end of the light projection module string to the light projection module located at the other end thereof and an adjacent module connection wire for connecting only the adjacent light projection modules, wherein each light projection module making up the light projection module string is electrically connected to the light projection signal transmission member. 
   This multi-beam photoelectric sensor comprises a photo-detector string constituting a light-receiving module string including a plurality of aligned light-receiving modules having an integration of a light-receiving optical system for one optical axis, a light-receiving circuit for one optical axis and flip-flops corresponding to one stage of shift register, and an optical signal transmission member including a common conduction wire for uniformly connecting from a light-receiving module located at an end of the light-receiving module string to the light-receiving module located at the other end thereof and an adjacent module connection wire for connecting only the adjacent light-receiving-modules, wherein each light-receiving module making up the light-receiving module string is electrically connected to the light-receiving signal transmission member. 
   Further, the flip-flops in the adjacent light projection modules are connected in cascade to each other by the adjacent module connection wire thereby to make up a shift register and so are the flip-flops in the adjacent light-receiving modules. 
   In response to the data sequentially sent by the shift register, each light projection module making up the light projection module string and each light-receiving module making up the light-receiving module string are sequentially operated. 
   With this configuration, the light projection module and the light-receiving module each accommodate not only an optical system (the light projection optical system or the light-receiving optical system) for one optical axis but also flip-flops corresponding to one stage of the shift register and the electrical circuit (the light projection circuit or the light-receiving circuit) for one optical axis. The flip-flops in the adjacent light projection modules and the flip-flops in the adjacent light-receiving modules are respectively connected in cascade by the adjacent module connection wires thereby to make up a shift register. Based on the presence or absence of a bit in the shift registers, the optical axis is selectively validated and a plurality of optical axes of the light curtain are sequentially activated. Thus, the desired number of single-beam modules (the light projection modules or the light-receiving modules) are repeatedly arranged at the desired intervals, and connected to each conduction wire (the common conduction wire and the adjacent module connection wire) of the signal transmission member (the light projection signal transmission member or the light-receiving signal transmission member). Regardless of the number of optical axes, therefore, the light curtain can be fabricated by concentrating at least the required parts used for each optical axis in the light projection module and the light-receiving module. Specifically, the number of part types can be reduced. A stock of different circuit boards corresponding to the number of a plurality of types of optical axes is not of course required. Further, with regard to the types of members not used repeatedly for each optical axis, the signal transmission member is cut to an appropriate length, while the columnar case, the light projection columnar member and the light-receiving columnar member are cut to an appropriate length using a member (an extrusion forming member, for example) to secure the same shape of the section perpendicular to the length of the column at any longitudinal position of the column or a cyclic member along the direction of column length. In this way, the number of types of parts can be reduced to minimum. 
   Also, the signal transmission member may be an integration of the common conduction wire and the adjacent module conduction wire while maintaining the insulation from each other. 
   With this configuration, the job is facilitated to electrically connect the light projection signal transmission member with the light projection module or the light-receiving signal transmission member with the light-receiving module. Especially, the adjacent module connection wire, if not integrated, is only a plurality of separate short wires, and therefore numerical control or the job to handle is bothersome. If integrated, on the other hand, they can be easily handled as one substantial signal transmission member, and the number of wires can also be positively, easily grasped according to the length of the signal transmission member. 
   At the same time, the light projection signal transmission member may be a flat cable having a plurality of core wires, specified ones of which are segmented by a plurality of punched holes, and specific ones of the core wires may also be used as adjacent module connection wires for connecting the adjacent modules. In similar fashion, the light-receiving signal transmission member may be a flat cable having a plurality of core wires, specified ones of which are segmented by a plurality of punched holes, and specific ones of the core wires may also be used as adjacent module connection wires for connecting the adjacent modules. 
   The employment of this flat cable can easily realize the common conduction wire and the adjacent module connection wire easily on the flat cable simply by forming the punched holes at appropriate pitches on a specified core wire and segmenting it. 
   Alternatively, the light projection optical system includes a light projection element, and the circuit parts corresponding to the light projection element, the light projection circuit and the flip-flop are accommodated in an IC package, while the lead pins of the IC package are used as pressure contact lead pins for connecting the flat cable, so that the IC package can be connected under pressure on the flat cable. In similar fashion, the light-receiving optical system includes a light-receiving element, and the circuit parts corresponding to the light-receiving element, the light-receiving circuit and the flip-flop are accommodated in an IC package, while the lead pins of the IC package are used as pressure contact lead pins for connecting the flat cable, so that the IC package can be connected under pressure on the flat cable. 
   With this configuration, without any socket structure on the side of the flat cable, the IC package can be easily connected at an arbitrary position on the flat cable, so that the length of the light projection/light-receiving columnar member and the number and pitches of optical axes can be changed in more versatile way. 
   The light projection module is integrated through the optical part holder with the lens member making up the light projection optical system having an optical axis aligned with that of the IC package accommodating the optical element. In the IC package, at least the light projection element is mounted on the lead frame, which is formed integrally as the same member as the lead pins, the bent portion of each lead pin is formed with a positioning hole, and the optical part holder is formed with a positioning protrusion at a position corresponding to the positioning hole formed at the bent portion of each lead pin. 
   Similarly, the light-receiving module is integrated through the optical part holder with the lens member making up the light-receiving optical system having an optical axis aligned with that of the IC package accommodating the optical element. In the IC package, at least the light-receiving element is mounted on the lead frame, which is formed integrally as the same member as the lead pins, the bent portion of each lead pin is formed with a positioning hole, and the optical part holder is formed with a positioning protrusion at a position corresponding to the positioning hole formed at the bent portion of each lead pin. 
   With this configuration, in the case where the IC package is mounted on the flat cable, the optical element (the light projection element or the light-receiving element) can be set in position with respect to the lens member without using the outer shape of the mold of the IC package or the like in such a manner that the positioning hole formed in the bent portion of each lead pin coincides with the positioning protrusion of the optical part holder, thereby improving the positioning accuracy. 
   In the process, the positioning hole may be formed in the bent portion of the lead pin. In this configuration, the IC package is defined as the upper member and the flat cable as the lower member. Then, the lower side of the inner periphery of the hole works as a pad for sticking each lead pin into the flat cable, while the side of the inner periphery existing in the plane perpendicular to the vertical direction works as a positioning contactor in the longitudinal and lateral directions. When sticking the IC package into the flat cable, therefore, the lead pin is pressed down from just above and therefore hardly displaced. This leads to the advantage that even a slight displacement of the optical element on the lead frame hardly occurs and the right optical axis is maintained. 
   The positioning hole, if rectangular in shape, can be configured of linear sides in all of the longitudinal, lateral and vertical directions. 
   In the light projection signal transmission member, the common conduction wire for uniformly connecting from the light projection module located at an end of the light projection module string to the light projection module located at the other end thereof includes a light projection current supply wire, a shift clock wire and a ground wire. At the same time, one of the wires between the adjacent modules may be connected with the D input terminal of the flip-flop and the other with the Q output terminal of the flip-flop. Similarly, in the light-receiving signal transmission member, the common conduction wire for uniformly connecting from the light-receiving module located at an end of the light-receiving module string to the light-receiving module located at the other end thereof includes a light-receiving current supply wire, a shift clock wire and a ground wire. At the same time, one of the wires between the adjacent modules may be connected with the D input terminal of the flip-flop and the other with the Q output terminal of the flip-flop. 
   With this configuration, the electrical circuit in the IC package can be appropriately operated-simply by appropriately designing the arrangement of the terminal pins of the IC package. 
   According to this invention, the desired number of individual single-beam modules (the light projection modules or the light-receiving modules) are arranged repeatedly at the desired intervals with each other and connected to the conduction wires (the common conduction wire and the adjacent module conduction wires) of the signal transmission member (the light projection signal transmission member or light-receiving signal transmission member). Without regard to the number of optical axes, therefore, the light curtain can be fabricated while the required parts used for at least each optical axis are concentrated in the light projection module and the light-receiving module. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a perspective view of the appearance of the light projection (or light-receiving) columnar member according to the invention. 
       FIG. 2  shows a perspective view as taken from the obverse surface of the sensor assembly. 
       FIG. 3  shows a perspective view as taken from the reverse surface of the sensor assembly. 
       FIG. 4  shows an exploded perspective view of the sensor assembly. 
       FIG. 5  shows an exploded perspective view of the multi-beam assembly. 
       FIG. 6  shows an exploded perspective view (No.  1 ) of the single-beam optical module. 
       FIG. 7  shows an exploded perspective view (No.  2 ) of the single-beam optical module. 
       FIG. 8  shows a sectional view of the (integrated-type) single-beam optical module. 
       FIG. 9  shows a sectional view showing the internal structure of the packaged optical IC. 
       FIG. 10  shows a diagram (No.  1 ) for explaining the positioning structure of the optical part holder and the packaged optical IC. 
       FIG. 11  shows a diagram (No.  2 ) for explaining the positioning structure of the optical part holder and the packaged optical IC. 
       FIG. 12  shows a diagram (No.  3 ) for explaining the positioning structure of the optical part holder and the packaged optical IC. 
       FIG. 13  shows a diagram for explaining a modification of the single-beam optical module. 
       FIG. 14  shows a sectional view showing the connection between the flat cable and the pressure contact terminal pins. 
       FIG. 15  shows a diagram for explaining the structure for holding the flat cable. 
       FIG. 16  shows an exploded perspective view showing the state before assembling the shield member. 
       FIG. 17  shows a diagram for explaining the structure for conduction between the shield member and the support frame. 
       FIG. 18  shows an exploded perspective view showing the state after assembling the shield member. 
       FIG. 19  shows a perspective view showing the structure of the circuit part assembly. 
       FIG. 20  shows a diagram for explaining the front seal structure of the columnar case. 
       FIG. 21  shows a sectional view showing the light projection (or light-receiving) columnar member. 
       FIG. 22  shows a diagram (No.  1 ) for explaining a modification of the shield structure. 
       FIG. 23  shows a diagram (No.  2 ) for explaining a modification of the shield structure. 
       FIG. 24  shows a diagram showing a general circuit configuration of the multi-beam photoelectric sensor according to the invention. 
       FIG. 25  shows a time chart showing the operation of the circuit as a whole. 
       FIG. 26  shows a diagram for explaining the timing of the shift clock. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of the invention is explained in detail below with reference to the accompanying drawings. A perspective view of the appearance of a light projection (or a light-receiving) columnar member according to this invention is shown in  FIG. 1 . As shown in  FIG. 1 , the multi-beam photoelectric sensor according to this invention is used with a light projection columnar member and a light-receiving columnar member  10  arranged in opposed relation to each other. 
   The case of the columnar member  10  includes a columnar case body  101 , an end cap  102  for closing up an end opening of the columnar case body, an end cap  103  for closing up the other end opening, and a front plate  104  for closing up the front side. As described in more detail later, the columnar case body  101 , the end caps  102 ,  103  are made of metal and have a substantially U-shaped section. The front plate  104  is formed of plastics transparent to the light used. A sensor assembly  10 A is accommodated in the columnar member  10 . 
   A perspective view of the sensor assembly taken from the obverse surface thereof is shown in  FIG. 2 , and a prospective view of the sensor assembly taken from the reverse surface thereof in  FIG. 3 . As apparent from these drawings, the sensor assembly  10 A is configured mainly of a multi-beam assembly  200 A, and a circuit part assembly  300  screwed to the reverse surface of the multi-beam assembly. As described in detail later, the multi-beam assembly  200 A is built around a multiplicity of single-beam optical modules aligned integrally with each other. The circuit part assembly  300 , on the other hand, is configured mainly of a circuit board having mounted a CPU or the like thereon. In these drawings, numeral  400  designates a connector part assembly. 
   An exploded perspective view of the sensor assembly is shown in  FIG. 4 .  FIG. 4  also shows the case body  101 , the end caps  102 ,  103  and the front plate  104  already explained above. 
   As explained above, the case for accommodating the sensor assembly  10 A includes the columnar case body  101  having a substantially U-shaped cross section, the end caps  102 ,  103  similarly having a substantially U-shaped cross section for closing up the two end openings, respectively, and the front plate  104  for closing up the front opening. 
   More specifically, an end of the columnar case body  101  is closed up by the end cap  102  through a seal member  105  and fixed by screws  110 . In similar fashion, the other end of the columnar case body  101  is closed up by the end cap  103  through a seal member  106  and fixed by screws  112 . A plug  109  is inserted into the end cap  102  and fixedly screwed. The forward end of an electrical cord  107  drawn out of the plug  109  has an inter-cord connector  108  at the forward end thereof. This electrical cord  107  is used for connecting one or at least two light projection (or light-receiving) columnar members  10 . 
   On the end cap  103  at the other end, on the other hand, a socket  111  corresponding to the plug  109  is fixed through screws  113 . On the front opening of the columnar case having a substantially U-shaped cross section configured in this manner, the front plate  104  is fixed by adhesive through rubber packings  120 , adhesive sheets  121 , seal members  116 ,  117 ,  118 ,  119  and insulating sheets  114 ,  115 . The multi-beam assembly  200 A includes as many single-beam optical modules  200  as the optical axes, a flat cable  220 , as many cable holders  230  as the optical axes and a support frame  250 . 
   An enlarged exploded perspective view of the multi-beam assembly is shown in  FIG. 5 .  FIG. 5  shows the portion of the multi-beam assembly corresponding to four optical axes. As apparent from  FIG. 5 , the single-beam optical modules  200  each include several optical parts with the lens members  201  combined and unified by the optical part holders  203  of resin, and as described in detail later, pressure contact terminal pins  205   a  are projected from the lower surface thereof. 
   The flat cable  220  accommodates a plurality of parallel core wires under a resin band cover and has the length adjustable arbitrarily by cutting with scissors or cutter. This example has eight core wires including a first core wire  220 - 1 , a second core wire  220 - 2 , a third core wire  220 - 3 , a fourth core wire  220 - 4 , a fifth core wire  220 - 5 , a sixth core wire  220 - 6 , a seventh core wire  220 - 7 , an eighth core wire  220 - 8 . Among them, the fifth core wire  220 - 5  used both for the D input and the Q output of the D-type flip-flop is segmented by equidistant-punched holes  220 - 5   a . This is by reason of the fact that although the other core wires can be shared by a plurality of single-beam optical modules  220 , the fifth core wire  220 - 5  is required to be used for both the D input and the Q output of the D-type flip-flop in the single-beam optical module  200 . 
   The cable holder  230  is a resin integrated molded product and includes centrally located backings  230   a  each having corrugated grooves on the surface thereof, and a four upright portions  230   c ,  230   c ,  230   c ,  230   c  erected from the four corners of the backing  230   a . The upright portions  230   c  are each formed with a protrusion  230   d . The protrusion  230   d , as described in detail later, is engageably fixed in the recess  250   c  formed at the left and right edges of each upright portion  250   a  on a support frame  250 . 
   The support frame  250  is a metal product (such as phosphor bronze) so shaped that a plurality of parts having a channel-shaped section are connected in the longitudinal direction. A recess  250   b  is formed at each of left and right edges of each pair of the opposed upright portions  250   a ,  250   a  having the channel-shaped portions. The recesses  250   b  are adapted to engage the protrusions  230   d  formed on the upright portions  250   c  of the cable holder  230 . Also, a hole  250   c  is formed at the root of each upright portion  250   a  of the support frame  250 . This hole  250   c  is fitted on the corresponding protrusion  230  formed on the lower surface of the cable holder  230  to set both of them in position. 
   As apparent from the foregoing description, the cable holders  230  are mounted on the opposed upright portions  250   a ,  250   b  formed on the support frame  250 , so that the cable holders  230  are fixed in position at equal pitches. The flat cable  220  is placed on the backings  230   a  of the cable holders  230 , and the single-beam optical modules  200  are laid on the assembly and pressed from above. Thus, the electrical conduction is secured between the single-beam optical modules  200  and the flat cable  220 . 
   What is important is, as explained in detail later, that the optical parts (the light-emitting element and the light-receiving element), the drive circuits thereof and all the electrical circuit elements such as the D-type flip-flops corresponding to one stage of shift register are accommodated in the optical part holders  203 , and therefore the longitudinal mounting position of the flat cable  220  of each single-beam optical module  200  is not restricted in any way. Thus, the number and pitches of the adjacent pairs of the opposed upright portions  250   a ,  250   a  formed on the support frame  250  can be freely set. At the same time, the number and pitches of the adjacent pairs of the opposed upright portions  250   a ,  250   a  directly correspond to the number and pitches of optical axes of the multi-beam photoelectric sensor. According to the invention, therefore, the design freedom of the number and pitches of optical axes is extremely improved. 
   Next, several specific configurations of the single-beam optical module  200  are explained. An exploded perspective view (No.  1 ) of the single-beam optical module is shown in  FIG. 6 . In this case, the single-beam optical module  200  includes a lens member  201 , a trap  202 , an optical part holder  203 , a shield plate  204  and a packaged optical IC  205 . In  FIG. 6 , numeral  201   a  designates a protrusion for positioning the lens member, numeral  204   a  a hole for shaping the beam section, numeral  205   a  pressure contact terminal pins and numeral  205   b  a dual in-line package (DIP) 
   The lens member  201  is what is called the plastic lens, and has a positioning protrusion  201   a  formed on one side thereof. The trap  202  corresponds to the lens barrel of the optical system and has the axial center thereof aligned with that of the lens member  201 . The optical part holder  203  is an integrated plastic molded product accommodating the lens member  201  and the trap  202  coaxially arranged with each other. On the bottom surface of the optical part holder  203 , there are a shield plate  204  and the packaged optical IC  205  laid one on the other. A specific mounting structure is explained in detail later. The shield plate  204  functions as a shield against the packaged optical IC  205 , and is configured of, for example, a metal part of phosphor bronze. A beam section shaping hole  204   a  is formed at about the central part of the shield plate  204 . 
   The packaged optical IC  205  has a dual in-line package (DIP)  205   b  of transparent resin. The pressure contact terminal pins  205   a  are projected downward and supported from the two edges of the dual in-line package  205   b . In this way, the concept of using the pressure contact pin  205   a  as each terminal pin of the dual in-line package  205   b  is a very novel idea unique to the inventors. The pressure contact terminal pins  205   a  are of course used as a connector for connecting the boards to each other as well as the legs of the packaged IC. Nevertheless, with this configuration in which the pressure contact terminal pins  205   a  are used as the terminal pins of the packaged optical IC  205  and inserted into the flat cable  220  so that the packaged optical IC  205  can be mounted at an arbitrary position along the length of the flat cable  220 , the freedom of arranging the optical elements (the light-emitting element or the light-receiving element) is extremely improved for various optical devices including the multi-beam photoelectric sensor. 
   As explained later with reference to  FIG. 24 , the packaged optical IC  205  accommodates the optical elements (the light-emitting elements or the light-receiving elements), the drive circuits for the optical elements and the D-type flip-flops for sequentially operating the drive circuits. 
   A specific example of these internal circuits is shown in  FIG. 24 . As apparent from  FIG. 24 , the light projection columnar member accommodates a circuit  20 , and the light-receiving columnar member a circuit  30 . The circuit  20  includes D-type flip-flops (hereinafter referred to as D-type FFs)  21  making up one stage of shift register, drive circuits  22  each connected with the Q output of the corresponding D-type flip-flop  21 , and light-emitting elements  23  driven by the output of the drive circuits  22 . A multiplicity of D-type flip-flops  21  connected with each other make up a shift register, with the result that the circuits  20  are sequentially turned on (activated) one by one. 
   The circuit  30 , on the other hand, includes light-receiving elements  31 , amplifier circuits  32  for amplifying the output of the light-receiving elements  31 , D-type flip-flops (hereinafter referred to as the D-type FFs)  34  making up one stage of shift register, and analog switches  33  interposed on the output side of the amplifier circuits  32  and turned on/ff by the Q output of the D-type flip-flops  34 . Also in this case, the D-type flip-flops  34  are connected with each other to make up a shift register. Thus, the individual D-type flip-flops are sequentially turned on one by one. 
   As described above, according to this invention, the circuit  20  or  30  is accommodated in the packaged optical IC  205  and integrated as a single-beam optical module  200 . The single-beam optical module according to the invention accommodates the circuit parts as well as the optical parts which are used for each optical axis. Regardless of the number of optical axes, therefore, an optical curtain can be fabricated by concentrating the parts required for at least each optical axis, in the light projection module or the light-receiving module. In this way, the number of types of the parts can be reduced. 
   This advantage of the improved design freedom is derived from the fact that the circuit  20  or  30  shown in  FIG. 24  is accommodated in the single-beam optical module. It will be understood, therefore, that the circuit  20  or  30  thus accommodated is not necessarily an integrated packaged optical IC. 
   Specifically, according to the invention, the circuit  20  or  30  shown in  FIG. 24  may be placed on a small dedicated circuit board and accommodated in the single-beam optical module  200 . Alternatively, the flat cable can exhibit its function sufficiently with two parallel conduction patterns, and therefore can be replaced with a flexible circuit board of an appropriate length, if any. In such a case, a free connection structure such as a through hole connection can be employed in order to mount and secure the electrical conduction of the single-beam optical modules at arbitrary positions of the conductor pattern on the flexible board. 
   An exploded perspective view (No.  2 ) of the single-beam optical module is shown in  FIG. 7 . In this case, a mask print  205   c  having a window hole  205   d  is arranged on the upper surface of the dual in-line package  205   b . The beam shaping function can be secured also by the mask print  205   c  and the window hole  205   c . The mask print  205   c  can avoid the intrusion of a noise component into the built-in optical element while using the transparent resin as a package material. 
   A sectional view of the single-beam optical module (integrated type) is shown in  FIG. 8 . In this case, unlike in  FIGS. 6 and 7 , the individual separate parts are not accommodated in the optical part holder  203 , but coupled integrally with each other in advance by insertion molding. In  FIG. 8 , numeral  205   a  designates pressure contact terminal pins, numeral  205   e  a lead frame, numeral  206  a package with a lens, numeral  206   a  a lens structure, numeral  207  a mask member, numeral  208  a slit and numeral  209  an optical element. 
   As apparent from  FIG. 8 , in this case, the optical element  209  and other circuit parts are mounted on the lead frame  205   c  inserted in the package  206  with a lens, and integrally molded by resin together with the lens structure  206   a.    
   Next, a sectional view showing the internal structure of the packaged optical IC used for the structure of  FIGS. 6 and 7  is shown in  FIG. 9 .  FIG. 9   a  shows a lead frame mount type, and  FIG. 9   b  a board mount type. 
   As explained above, in any of the types, the packaged optical IC having the pressure contact terminal pins  205   a  is a quite novel structure and a unique creation by the present inventors. 
   In the packaged optical IC  205  of lead frame mount type shown in  FIG. 9   a , the optical element  205   j  and the circuit part  205   k  are mounted directly on the lead frame  205   i  integrated with the pressure contact terminal pins  205   a . Especially in the example under consideration, a reflector structure  205   h  recessed in the shape of bowl is formed by pressing on the lead frame  205   i , and the optical element  205   j  is placed at the central part of the bottom thereof to improve the light projection or the light-receiving efficiency. Numeral  205   g  designates a transparent seal resin. Also, the shape of the forward end of each pressure contact terminal pin  205   a  is well known. Specifically, this forward end is forked into two left and right branches with sharp forward edges, while the core wire of the flat cable is pressure fitted into the slit between the two branches to assure electrical conduction therebetween. Further, in this example, a band-shaped conduction path is appropriately punched in the lead frames  205   i  in flat form thereby to secure the conduction paths for the individual circuit parts and the optical elements. 
   In the packaged optical IC of board mount type shown in  FIG. 9   b , on the other hand, a two-side circuit board  205   l  is arranged in addition to the lead frame  205   i , and the optical element  205   j  and the circuit part  205   k  are mounted on the circuit board  205   l . At the same time, the conduction pattern adapted to be connected to each of the pressure contact terminal pins  205   a  is formed on the lower surface of the circuit board  205   l , and soldered with each lead frame  205   i . In this way, the electric conduction is assured between the individual pressure contact terminal pins  205   a , the optical element  205   j  and the circuit part  205   k.    
   In this case, the provision of the board  205   l  in addition to the lead frames  205   i  increases the rigidity. This leads to the advantage that the rigidity of the circuit board  205   l  prevents the optical element  205   j  from being displaced even under the pressure of connecting the pressure contact terminal pins  205   a.    
   Specifically, in the lead frame mount type shown in  FIG. 9   a , the optical element  205   j  is mounted on the lead frame  205   i , and therefore, the inner lead frame is displaced under the pressure applied to the pressure contact terminal pins  205   a , thereby often leading to the problem of slight displacement of the optical element  205   j . In the board mount type shown in  FIG. 9   b , on the other hand, the position of the optical element  205   j  is advantageously prevented from being displaced even when the pressure contact terminal pins  205   a  are displaced by the rigidity of the board  205   l.    
   Next, the positioning structure of the optical part holder and the packaged optical IC is explained. As shown in  FIG. 9   a , assume that the packaged optical IC  205  is used in which the optical element  205   j  and the circuit part  205   k  are mounted on the lead frame  205   i  and insertion molded using the seal resin  205   g , while the terminal pins projected from the lead frame  205   i  are formed as the pressure contact terminal pins  205   a , and that this packaged optical IC  205  is mounted on the lower surface of the optical part holder  203 , as shown in  FIGS. 6 and 7 . The position of the optical element  205   j  in the packaged optical IC  205  is required to be matched accurately with the optical axis of the lens  201  placed in the optical part holder  203 . 
   In a conceivable method to accomplish this configuration, a positioning protrusion is formed on the dual in-line package  205   b  of the packaged optical IC  205  and fitted in the corresponding positioning recess formed on the optical part holder  203 . The employment of this positioning structure, however, could not necessarily match the position of the optical element  205   f  accurately with the optical axis of the lens  201  due to the forming error of the dual in-line package  205   b.    
   According to this invention, instead of the package  205   b  of the packaged optical IC  205 , a given part of the lead frame projected from the package  205   b  and the optical part holder  203  are set in position with each other, thereby making it possible to set the optical element  205   f  in the package  205   b  and the optical axis of the lens member  201  in position accurately with each other. 
   The diagrams (Nos.  1  to  3 ) for explaining the positioning structure of the optical part holder and the packaged optical IC are shown in  FIGS. 10 to 12 , respectively. In  FIG. 10 , the packaged optical IC  205  and the optical part holder  203  are separated slightly in vertical direction from each other. As apparent from this diagram, the lower surface edges on the left and right sides of the optical part holder  203  are formed with a plurality of engaging protrusions  203   b  directed downward. 
   At the root (bent corner) of each pressure contact terminal pin  205   a  projected downward from the packaged optical IC  205 , on the other hand, a plurality of engaging holes  205   f  are formed correspondingly to a plurality of engaging protrusions  203   b , respectively, of the packaged optical IC  205 . As shown in  FIG. 11 , once the package IC  205  is mounted completely on the optical part holder  203 , the plurality of the engaging protrusions  203   b  of the package  205   b  are fitted in the engaging holes  205   f  located at the root of the pressure contact terminal pin  205   a , so that the package  205   b  and the root of the pressure contact terminal pins  205   a  are accurately set in position. 
   Assume that the package  205   b  and the root of the pressure contact terminal pins  205   a  are set in position in this way. The pressure contact terminal pins  205   a  are integrated with the lead frame  205   i , on which the optical element  205   j  is mounted, and the mounter accuracy maintains the optical element  205   j  at an accurate mounting position relative to the lead frame  205   i . As far as the positioning accuracy between the optical part holder  203  and the lens  201  and the forming accuracy of the engaging protrusions  203   b  with respect to the optical part holder  203  are correctly controlled, therefore, the optical element  205   j  and the optical axis of the lens member  201  in the packaged optical IC  205  can be accurately set in position with each other. 
   In the process, the positioning holes  205   f  may be rectangular and formed in the bent portions of the lead pins. With this configuration, of all the sides of the inner periphery of the rectangular hole including the lower side, the upper side, right side and the left side, the horizontal lower side functions as a pad for piercing the lead pins, while the right and left sides work as a contact for positioning in lateral directions. As a result, when piercing an electronic part in the flat cable, the lead pins pushed from just above are hardly displaced. This substantially prevents even a slight displacement of the optical element on the lead frame hardly, thereby advantageously maintaining the performance to keep right optical axes. 
   The positions of the engaging holes  205   f  formed at the root of the pressure contact terminal pins  205   a  are shown in more detail in  FIG. 12 . Specifically, the engaging holes  205   f  are each accurately formed at the corners of the bent portion between the lead frame  205   i  and the pressure contact terminal pins  205   a . Once the packaged optical IC  205  is mounted accurately on the lower surface of the optical part holder  203  as shown in  FIG. 11 , therefore, the engaging protrusions  203   b  come into contact with the upper end of the vertical extension  205   m  of each pressure contact terminal pin  205   a . In the case where the forward end of the pressure contact terminal pin  205   a  is stuck on the flat table and pressured to break the covering of the flat table, therefore, pressure is exerted on the lower surface of the inner periphery of the engaging holes  205   f  from just above. The downward pressure applied to the optical part holder  203 , therefore, is transmitted efficiently to the vertical extension  205   m  of each terminal pin  205   a , resulting in the advantage that the pressure contact terminal pins  205   a  are difficult to displace. 
   Specifically, the displacement of the vertical extension  205   m  causes the chain reaction in which the lead frame  205   i  in the packaged optical IC  205  is displaced, which in turn may displace the optical element  205   j  mounted thereon. The relative positions of the engaging protrusions  203   b  and the engaging holes  205   f  described above, however, makes it difficult to displace the pressure contact terminal pins  205   a  thereby advantageously suppressing the displacement of the optical element. 
   A diagram for explaining the single-beam optical module according to a modification is shown in  FIG. 13 .  FIG. 13   a  shows a case using receptacles or sockets for the pressure contact terminal pins, and  FIG. 13   b  an example of the application of receptacles or sockets for receiving springs. As explained above with reference to the circuit diagram of  FIG. 24 , the main feature of the single-beam optical module according to the invention resides in that the electrical circuit parts as well as the optical parts are accommodated and that the single-beam optical module can be easily mounted at an arbitrary longitudinal position on the flat cable or the flexible circuit board. 
   This fact, or especially the latter point described above, indicates that as long as the pressure contact terminal pins or universal contactors are projected from the bottom surface of the single-beam optical module, the optical part case or the circuit part assembly should be able to be accommodated in any form. By dividing the single-beam optical module into vertical halves and using the lower portion as a socket and the upper portion as a part case, therefore, the replacement for repair or maintenance can be facilitated. 
   From this standpoint, an example of design is shown in  FIGS. 13   a ,  13   b . In the case of  FIG. 13   a , the single-beam optical module  200  is similar to the one described above, although a socket  200 A is interposed between the single-beam optical-module  200  and the flat cable  220 . The upper surface of the socket  200 A is formed with holes  205 A- 1  to receive the pressure contact terminal pins  205   a  of the single-beam optical module  200  while pressure contact terminal pins  205 A- 2  are projected from the bottom surface of the socket  200 A to be pierced into each core wire of the flat cable. 
   In the case of  FIG. 13   b , on the other hand, a spring contactor (not shown) is projected from the bottom surface of the single-beam optical module  200 . Also, a socket  200 A is interposed between the single-beam optical module  200  and the flat cable  220 . The upper surface of the socket  200 A is formed with conductor patterns  205 A- 3  adapted for contact with the spring contactor, not shown, projected from the bottom surface of the single-beam optical module  200 . Each of the conductor patterns  205 A- 3  is electrically connected to the corresponding pressure contact terminal pin  205 A- 2  projected from the bottom surface, and the pressure contact terminal pins  205 A- 2  projected from the socket  200 A are pierced into the core wires of the flat cable  220  thereby to secure electric conduction. In this way, the single-beam optical module can assume any of various structures. 
   A sectional view of the connection between the flat cable and the pressure contact terminal pins is shown in  FIG. 14 . In  FIG. 14 , numeral  201  designates lens members, numeral  202  traps, numeral  205  packaged optical ICs, numeral  220  a flat cable, numeral  220   a  a bent portion of the flat cable, numeral  205   a  pressure contact terminal pins, and numeral  230  a cable holder. As apparent from  FIG. 14 , the pressure contact terminal pins  205   a  are pierced through the flat cable  220  and extend out of the lower surface thereof. In the process, each core wire of the flat cable  220  is pressure fitted into the slit at the forward end of the corresponding terminal pin  205   a  thereby to secure electrical conduction between them. The flat cable  220  is bent at the extreme end portion  220   a  of the single-beam optical modules in alignment, and folded along the bottom of the cable holder  230 . 
   A diagram for explaining the structure for holding the flat cable is shown in  FIG. 15 . In  FIG. 15 , numeral  201  designates a lens member, numeral  203  an optical part holder, numeral  230  a cable holder, numeral  203   d  engaging hooks of the optical part holder, numeral  230   e  engaging steps of the cable holder, numeral  220   a  bent portions of the flat cable, numeral  220   b  a cable connector and numerals  220 - 1  to  220 - 8  first to eighth core wires, respectively, of the flat cable. 
   As apparent from  FIG. 15 , the flat cable  220  is held sandwiched between the bottom of the optical part holder  203  in an upper position and the backing  230   a  of the cable holder  230  in a lower position. The optical part holder  203  and the cable holder  230  are firmly fixed by engagement between the engaging hooks  203   d  and the steps  230   e.    
   A structure of a shield member is explained which is used to avoid the effect of noises of the multi-beam photoelectric sensor in whatever adverse noisy environment of a production field. An exploded perspective view of the state before assembling the shield member is shown in  FIG. 16 , a diagram for explaining the structure for conduction between the shield member and the support frame is shown in  FIG. 17 , and an exploded perspective view of the state after assembling the shield member is shown in  FIG. 18 . 
   As shown in  FIG. 16 , the feature of the multi-beam photoelectric sensor according to the invention is that a plurality of single-beam optical modules can be arranged, without any special complicated processing, at arbitrary longitudinal positions on parallel conductive members such as flat cables. This advantage, however, constitutes a disadvantage at the same time. Specifically, a space  250   e  is developed in the gap between the adjacent single-beam optical modules, and the parallel conductor pattern is exposed to this space  250   e . Electromagnetic noises which may be generated from the case front, therefore, have a direct effect on the conductor pattern thereby causing the intrusion of noises. 
   In the example shown in  FIG. 16 , the provision of the upper surface shield member  260  closes up the gaps between the modules, thereby preventing the intrusion of noises into the parallel conductor patterns (such as the core wires of the flat cables) 
   As shown in  FIG. 16 , the upper surface shield member  260  includes a central portion  260   a  extending along the direction of module arrangement, and side extensions  260   b ,  260   b  extending laterally from the two side edges. Engaging hooks  260   c ,  260   c  are formed between the side extensions  260   b ,  260   b . This upper surface shield member  260  is placed on the single-beam optical module assembly. Then, the engaging hooks  260   c  engage the upper surface corners of the optical part holders  203  of the single-beam optical modules, so that the positions thereof are set. At the same time, the side extensions  260   b  close up the spaces  250   e  between the modules thereby to perform the shield operation as required. 
   In the process, as shown in  FIG. 17 , the side extensions  260   b  have the property as a spring in such a direction as to expand in the left and right directions as indicated by arrows in  FIG. 17 , whereby the forward end of each side extension  250   b  comes into contact with the inner surface of the corresponding upright portion  250   d  of the support frame  250  thereby to form contact conductor portions  260   e . As a result, the eddy current generated under the effect of the electromagnetic noises is saved toward the support frame  250  by the operation of the contact conductor portions  260   e  thereby to enhance the shield effect. As shown in  FIG. 18 , after assembling the shield member, the spaces between the modules are completely closed up by the side extensions  260   b  and the central portion  260   a , although the window holes  260   d  secure the optical axis of the projected or received light. 
   As described above, in the example shown in  FIGS. 16 to 18 , the provision of the upper surface shield member  260  of metal (such as phosphor bronze) completely closes up the spaces  250   e  between the adjacent modules, and the intrusion of noises into the underlying conductor pattern (such as a flat cable) is positively shut off. 
   Next, a perspective view of the structure of the circuit part assembly is shown in  FIG. 19 . As shown in  FIG. 19 , the circuit part assembly  300  includes a CPU board  301 , a connector board  302 , and a board holder  303 . The board holder  303  holds the CPU board  301  and the connector board  302  on the lower surface thereof, and holds the multi-beam assembly  200 A on the upper surface thereof. 
   The circuit  40  or the circuit  50  shown in  FIG. 24  is mounted on the CPU board  301 . The circuit  40  of the light projection columnar member has mounted thereon a processing circuit (CPU)  41 , a gate circuit  42 , a display circuit  43 , an input/output circuit  44  and a communication circuit  45 . In similar fashion, the circuit  50  of the light-receiving columnar member has mounted therein a processing circuit (CPU)  51 , an amplifier circuit  52 , a display circuit  53 , an input/output circuit  54  and a communication circuit  55 . 
   The display circuits  43 ,  53  each have a light-emitting element for display. These light-emitting elements  301   a , as shown in  FIG. 19 , are arranged in appropriately spaced relation with each other at one side edge of the CPU board  301 . At each of the positions just above the light-emitting elements  301   a , a light conductor  303   e  extending in vertical direction is formed integrally with the board holder  303 . The forward end  303   f  of each light conductor  303   e  is exposed to the upper surface through the gap of the optical part holder  303 . As a result, in spite of the provision of the light-emitting elements  301   a  on the board, the light emitted from them is led upward by the light conductors  303   e  and released outside from the forward end  303   f  thereof, thereby exhibiting a superior visual recognizability. 
   The board holder  303  has a pair of support protrusions  303   a ,  303   b  in laterally opposed relation to each other. A groove  303   c  is formed between each adjacent support protrusions  303   a ,  303   b , and the corresponding portion of the optical part holder  203  is inserted into each groove  303   c , so that the optical part holder  203  is fixedly positioned on the upper surface of the board holder  303 . As a result, as explained above with reference to  FIG. 2 , a sensor assembly  10 A coupled with the circuit part assembly  300  on the lower surface of the multi-beam assembly  200 A is completed. 
   Next, a diagram for explaining the front seal structure of the columnar case is shown in  FIG. 20 . As shown in  FIG. 20   a , the front plate  104  closing the front opening of the case is formed of a light projection plate  104   a  of plastics or the like having a comparatively high rigidity and a photoconductive film  104   b  stacked on the reverse side of the light projection plate  104   a . As shown in  FIG. 20   b , the stack structure of the light projection plate  104   a  and the conductive film  104   b  is fitted in the front opening of the columnar case body  101 , and fixed by an adhesive tape or the like not shown. This arrangement of the conductive film  104   b  on the back of the light projection plate  104   a  can reduce the effect of noises on the internal parallel conductors (flat cable or the like). 
   Next, an end surface of the light projection (or light-receiving) columnar member is shown in  FIG. 21 . In  FIG. 21 , numeral  101  designates a columnar case body, numeral  104  a front plate, numeral  114  an insulating sheet, numeral  203  an optical part holder, numeral  220  a flat cable, numeral  230  a cable holder, numeral  302  a connector board, numeral  302   a  a connector, and numeral  303  a board holder. These parts explained above are accommodated in the columnar case body  102  in the manner shown, and the two ends thereof are closed up by the end caps  102 ,  103  as explained already. 
   Next, a first diagram for explaining a modification of the shield structure is shown in  FIG. 22 , and a second diagram for explaining the same in  FIG. 23 . As explained above, a space  250   e  develops between each adjacent single-beam optical modules  200 ,  200 , and noises are liable to intrude into the flat cable from the particular space. In the examples shown in  FIGS. 16 to 18 , as explained above, this space is covered with an upper surface metal shield plate  260  thereby to exhibit the shield function. In this case, however, each time the number of the optical modules connected changes, the upper surface shield plate  260  is required to be refabricated. In the example shown in  FIGS. 22 and 23 , in contrast, the spaces can be individually filled with a shield piece  273  or  274  or a dummy module  271  or  272 . With this configuration, the spaces between the modules can be shielded without regard to the number of the modules connected, as long as the pitches between the modules are constant. 
   An enlarged view of the dummy module  271  is shown in  FIG. 23   b . As shown in  FIG. 23   b , the dummy module  271  has a nonconductive body and metal legs  271   e ,  271   e  having the spring property projected from the lower surface of the nonconductive body. The module body is formed of a nonconductive member having an upper surface  271   a  and left and right side surfaces  271   b , and at the two ends thereof, four protrusions  271   c ,  271   c ,  271   d ,  271   d  are formed. The protrusions  271   c ,  271   c  are for push-down function and the protrusions  271   d ,  271   d  function as stoppers. This dummy module  217  is pushed into each inter-module space  250   e . Then, the push-down protrusions  271   c ,  271   c  are brought into contact with the corresponding portions of the support frame  250 , and coupled with the repulsive operation of the legs  271   e ,  271   e , the dummy module  271  closely attaches to the support frame  250  through the legs  271   e ,  271   e , while at the same time being fixed by the stopper steps  271   d ,  271   d.    
   The shield piece  273  is shown enlarged in  FIG. 23   a . As shown in  FIG. 23   a , the shield piece  273  is configured of a thin metal material (such as phosphor bronze) and has an upper surface plate  273   a  and side surface plates  273   b . The ends of the upper surface plate  273   a  are formed with left and right branches  273   c ,  273   c ,  273   d ,  273   d , which bite into the corresponding protrusions on the support frame from the upper surface thereof so that the shield piece  273  is mounted in the corresponding space. In  FIG. 23   a , the bent contactor  273   e  has the spring property and comes into contact with the inner surface of the support frame  250  thereby to secure the electric conduction between them. Numeral  273   e  designates a stopper protrusion to prevent the shield piece from coming off. 
   Returning to  FIG. 22 , the dummy module  272 , having a resin body of a similar structure to that of the dummy module  271 , is formed of a metal film covered on the outer surface of the resin body, and similarly includes the push-down protrusions  272   a  and the vertical stopper protrusions  272   b . Also, the shield piece  274  is a channel-shaped metal piece formed by the most simple pressing process, and has stoppers  274   a.    
   As described above, according to this invention, the gaps or spaces  250   e  between the adjacent modules are closed up by the dummy modules  271 ,  272  or the shield pieces  273 ,  274 , so that noises are prevented from intruding into the core wires of the flat cable from the particular gaps or spaces. In this individual mounting method, the gaps between the modules can be successfully shielded regardless of the number of optical axes simply by preparing several types of dummy modules or shield pieces in accordance with the pitches of the optical axes. 
   Finally, with reference to  FIGS. 24 and 25 , the general circuit of the multi-beam photoelectric sensor according to the invention is explained. As described above, the multi-beam photoelectric sensor according to the invention includes a circuit unit built in the light projection columnar member and a circuit unit built in the light-receiving columnar member. The light projection columnar member contains a circuit  20  corresponding to each optical axis and a circuit  40  corresponding to the CPU board. Similarly, the light-receiving columnar member contains a circuit unit  30  corresponding to each optical axis and a circuit unit  50  corresponding to the CPU board. 
   First, the light projection columnar member is explained. The circuit unit  20  is directly built in the single-beam optical module  200 . The circuit unit  20  may be so built in or accommodated by mounting the corresponding circuit part on each circuit board piece, or a packaged optical IC  205  may be configured as shown in  FIGS. 6 ,  7  and  9 . Also, the connection structure between each single-beam optical module  200  and the flat cable or the parallel conductor flexible board can be determined in accordance with the structure of the conductor pattern. 
   In the case where the parallel conductor member to be connected with a given single-beam optical module is the flat cable  220  as shown in  FIG. 5 , the connection structure employs the pressure contact terminal pins  205   a  as shown in  FIGS. 10 to 12 . In the case where the parallel conductor member is a flexible circuit board, in contrast, a spring-type contactor or a through-hole structure connectable at an arbitrary position on the conductor pattern can be employed. 
   Any way, the configuration should be preferably such that each single-beam optical module can be mounted, without any special complicated process, at an arbitrary longitudinal position on the parallel conductor member. This makes it possible to mount each single-beam optical module at an arbitrary longitudinal position on the parallel conductor member, and therefore improves the freedom of setting the pitches and the number of optical axes at the same time. As for the timing of the signals a to d and the waveform in  FIGS. 10 to 12 , refer to the time chart of  FIG. 25 . 
   The circuit  40  mounted on the CPU board, on the other hand, includes a processing circuit (CPU)  41 , a gate circuit  42 , a display circuit  43  and an input/output circuit  44 . Once a series of adjacent circuits  20  are connected through a parallel conductor such as a flat cable, a series of D-type flip-flops  21 ,  21 , . . . make up a shift register. Each drive circuit  6  is activated by the Q output of the corresponding D-type flip-flop  21  output in each stage, and the light-emitting elements  23  are turned on sequentially. At the same time, the drive timing is controlled by the signal d. 
   Each circuit  30  of the light-receiving columnar member is accommodated in the corresponding single-beam optical module by being mounted on the small circuit board piece or as a packaged optical IC as explained above. 
   Each circuit  30  includes a light-receiving element  31 , an amplifier circuit  32 , an analog switch  33  and a D-type flip-flop  34 . Also, the single-beam optical module and the parallel conductor member can be connected to each other either by a flat cable or by a flexible circuit board. As in the light projection, the adjacent single-beam optical modules are connected in a daisy chain through a conductor pattern thereby to constitute a shift register. In response to the Q output of the D-type flip-flop making up to the output of each stage, the analog gate  44  is opened, so that the output of the light-emitting element of each module is introduced into the processing circuit  51 . 
   As explained in detail above, according to an embodiment of the invention, each single-beam optical module of the multi-beam assembly  200 A is configured to accommodate not only the optical parts but also the parts of the circuits  20 ,  30  as well, while at the same time employing a one-touch connection structure between the optical module  200  and the parallel conductor member. Therefore, each single-beam optical module  200  can be mounted at an arbitrary longitudinal position on the parallel conductor member, thereby extremely improving the freedom of designing the pitches and the number of optical axes. 
   Also, the employment of the pressure contact terminal pins  205   a  as a terminal structure of the single-beam optical module  200  and the employment of the flat cable  220  as a corresponding parallel conductor member at the same time further facilitates the connection between them. Thus, the requirement for an arbitrary pitches and the required number of optical axes can be met in a versatile way. 
   In addition, the electrical circuit parts are accommodated as circuit board pieces or a packaged optical IC in the single-beam optical module  200 , and therefore both the yield and productivity are successfully improved. Especially in the case where the packaged optical IC  205  is used as a circuit part, the employment of the fitting structure between the engaging holes  205   f  at the root of the pressure contact terminal pins  205   a  and the engaging protrusions  203   b  of the optical part holder  203  can achieve a highly accurate positioning between the optical elements  205   f  in the package and the optical axes of the lens members  201 . 
   Also, the spaces generated between the adjacent single-beam optical modules arranged at arbitrary pitches on the parallel conductor member are closed by the upper surface shield member  260  or individually by the dummy modules  271 ,  272  or the shield pieces  273 ,  274 . In this way, the noises from the case front are positively prevented from intruding into the parallel conductors (such as the core wires of the flat cables) exposed to the spaces. 
   Further, especially in the case where the flat cable is used as a parallel conductor member, as shown in  FIG. 5 , the punched holes  220 - 5   a  are formed at predetermined intervals in the core wire  220 - 5  shared by the D input and the Q output of the D-type flip-flop and thus the core wire is segmented. As a result, two different terminal pins can be mounted on the same core wire, thereby making it possible to meet the requirement of the D-type flip-flop with the same complete parallel conductor pattern. Specifically, the adjacent core wires segmented are connected alternately to the Q output of the first-stage flip-flop and the D input of the next-stage flip-flop. In this way, the requirement of the circuit configuration can be met simply by setting two terminal pins on the same line in position.