Photoelectric sensor assembly with transparent housing an integrally molded lens

A low cost assembly comprising only three major components: a circuit board assembly, a molded plastic housing and a molded plastic cover. The plastic parts are transparent polycarbonate (natural "Lexan") wherein the housing has an integrally molded optical quality lens. Mounting features are integrally molded on the housing and cover. The circuit board assembly uses a common board, trace pattern and terminals and can be either a source or detector by appropriate selection of electronic components mounted to the board. A plurality of rounded bosses on the housing and larger round recesses in edges of the circuit board provide a light interference fit between housing and board to firmly hold the board in place and provide correct orientation of the board relative to the housing. The board may be readily removed and replaced for field repair of the sensor.

BACKGROUND OF THE INVENTION 
This invention relates to photoelectric sensors and in particular to 
through beam photoelectric sensors. More particularly, the invention 
relates to a low cost photoelectric sensor assembly for a through beam 
photoelectric sensor which may readily be repaired in the field. 
The use of sensors to monitor the presence or absence of an object, its 
position, or some other condition of the object in manufacturing and 
handling apparatus is steadily increasing, due largely to the availability 
of computers, microcomputers and the like which can quickly respond to the 
sensed conditions and make appropriate changes in the process. A piece of 
manufacturing or material handling apparatus may contain numerous sensors. 
Photoelectric sensing is a popular form of sensing for many applications. 
However, the cost of photoelectric sensors is a deterrent to using this 
form of sensor in the growing quantities conceivable for such 
manufacturing and material handling apparatus. Moreover, since most 
sensing applications are in manufacturing production lines, and since it 
is undesirable to shut down such production lines for repair of any 
element thereof, repair of most photoelectric sensors presently available 
comprises replacement of the sensor on the site. 
SUMMARY OF THE INVENTION 
This invention provides a photoelectric sensor assembly which is 
particularly low cost and of modular construction to permit field 
replaceability of the electronics of the device without need to replace 
the lens, housing, mounting block and other hardware elements that 
comprise a photoelectric sensor. The photoelectric sensor assembly of this 
invention comprises only three components plus mounting hardware such as 
screws and nuts. Two of the components are molded plastic members; the 
third component is a circuit board assembly which is substantially the 
same for either a source or detector assembly. One molded member is a 
housing molded of transparent plastic having optical characteristics when 
molded, the housing comprising an internal chamber open to one side of the 
housing and having a focusing lens molded integrally with the housing at a 
side opposite the open side of the chamber. The housing also includes a 
mounting block portion molded integrally therewith, the mounting block 
portion having a substantially semicylindrical recess in one side thereof 
and a pair of holes disposed at right angles to the axis of the 
semicylindrical recess. A circuit board having terminals connected thereto 
has a photoelectric sensor device of either the source or detector type 
selectively mounted thereon. Significant cost efficiency is realized by 
utilizing one circuit board for both the source and the detector module. 
The circuit board may be readily inserted or removed from the chamber of 
the housing and retained firmly in the chamber by light finger pressure to 
facilitate initial assembly and subsequent removal and replacement of the 
circuit board in the event repair becomes necessary. 
The other molded member is a cover for the open side of the housing, the 
cover overlying the circuit board and retaining the same in its assembled 
position. In a preferred embodiment, the cover also includes a clamping 
portion which is coextensive with the mounting block portion of the 
housing, the clamping portion having a semicylindrical recess complemental 
to that of the mounting block portion and a pair of holes transverse to 
the axis of the semicylindrical recess aligned with the holes in the 
mounting block. A pair of screws are provided for securing the clamping 
portion against the mounting block around a mounting bar or the like for 
mounting the sensor assembly to a structural member. The photoelectric 
sensor assembly of this invention thus comprises only three major distinct 
elements plus the mounting screws (and nuts, if required). A pair of the 
photoelectric sensor assemblies of this invention are utilized in 
combination, one comprising a light source and the other comprising a 
detector, to provide a through beam photoelectric sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, the photoelectric sensor assembly 2 of this 
invention comprises a molded transparent plastic housing 4 having a cover 
6 attached thereto by a pair of screws 8 which cooperatively receive 
threaded nuts 10 (FIG. 4). The material of housing 4 is a thermoplastic 
polyacrylic or polycarbonate that can be fabricated with optical 
characteristics. Preferably this material is a natural transparent 
polycarbonate sold by the General Electric Company under the trademark 
"Lexan". Housing 4 comprises a hollow chamber 4a (FIGS. 3, 4 and 6) open 
to the rear of the housing. The front wall of housing 4 adjacent chamber 
4a has focusing a lens portion 4b integrally molded therewith. The 
interior and exterior surfaces of lens portion 4b are formed with an 
optical quality by particularly polishing these areas of the mold die. A 
pair of ribs 4c extend along opposite interior side wall surfaces of 
chamber 4a from the closed end adjacent lens portion 4b to the open rear 
side thereof. The ends of ribs 4c adjacent the open side of housing 4 have 
stepped-down semicylindrical bosses 4d formed thereon providing a shoulder 
between the respective rib 4c and bosses 4d. A third boss 4d is formed on 
the face of a bottom wall 4e of the housing adjacent chamber 4a. The rear 
ends of the side walls of housing 4 have inwardly turned stub walls 4f 
(FIGS. 3 and 6) defining a gap 4g therebetween which extends under bottom 
wall 4e. A mounting block portion 4h extends downwardly along the front of 
housing 4. As seen in FIG. 3, mounting block portion 4h is substantially 
hollow, being defined by the side walls of housing 4 and having a central 
rib 4j. Each of the side walls and the central rib 4j have a substantially 
semicircular recess 4k which together define a semicylindrical recess in a 
rear face of the mounting block portion 4h. Immediately above and below 
the recess 4k in central rib 4j are holes 4m extending through the 
mounting block portion 4h from front to rear at substantially right angles 
to the axis for the semicylindrical recess. A hexagonal counterbore 4n is 
molded in the front face of mounting block portion 4h around the holes 4m. 
Cover 6 is a molded plastic member, also molded of transparent plastic such 
as the transparent polycarbonate of housing 4, although it could be molded 
of an opaque or translucent plastic without affect on the performance of 
the sensor assembly of this invention. The cover 6 is separately shown in 
perspective in FIG. 2 and in front elevation in FIG. 5. An upright 
rectangular portion 6a of the cover overlies the open rear side of housing 
4. Rectangular portion 6a has a rectangular rib 6b that projects into the 
chamber 4a around the periphery of the opening and stub walls 4f of 
housing 4 extend under the lower corners of the rib 4b to position the 
cover 6 in place on housing 4. A pair of diagonally disposed openings 6c 
are provided in rectangular portion 6a through which terminals of the 
circuit board project as will be described hereinafter. 
Cover 6 also comprises a lower clamping portion 6d which is coextensive 
with mounting block portion 4h when housing 4 and cover 6 are assembled 
together. Clamping portion 6d is similar to mounting block portion 4h in 
that it is substantially a hollow structure defined by a pair of outer 
sides of the cover 6 and has a central rib 6e. The outer sides and the 
central rib 6e each have substantially semicircular recesses 6f which 
together define a semicylindrical recess open to the front side of 
clamping portion 6d. Above and below the recess 6f in central rib 6e are a 
pair of holes 6g extending through the clamping portion 6d from front to 
rear at right angles to the axis for the semicylindrical recess and 
aligned with the holes 4m of mounting block portion 4k when cover 6 is 
positioned to housing 4. Hexagonal counter bores 6h (FIG. 4) are molded in 
the rear face of clamping portion 6d around the holes 6g. Screws 8 extend 
through the holes 6g into the counterbores 6h where hexagonal nuts 10 are 
received to be threadably engaged by screws 8. When the cover 6 and 
housing 4 are secured together by the screws 8 and nuts 10, the recesses 
4k and 6f cooperatively define a circular opening with the mating surfaces 
of the mounting block portion 4h and clamping portion 6d being spaced 
apart as shown in FIGS. 1 and 4. Thus the sensor assembly 2 may be 
assembled around or inserted over a mounting member such as a conduit, 
pipe or similar round bar 5 (shown in dot-dash lines in FIG. 1) having a 
diameter substantially equal to the circular opening defined by the 
recesses 4k and 6f and clamped firmly thereon by tightening the screws 8 
into the nuts 10. It will be appreciated that the screws 8 and nuts 10 can 
be assembled to the sensor assembly 2 in the reverse direction to that 
shown if so desired. 
A circuit board 12 is mounted in the chamber 4a prior to attaching the 
cover 6 to the housing 4. Circuit board 12 has a rectangular profile 
complemental to the interior profile of chamber 4a and is dimensioned to 
provide a minimal clearance in the opening. As seen in FIGS. 7, 8 and 10, 
circuit board 12 is provided with three semicircular recesses 12a in the 
bottom and two opposite side edges of the circuit board as oriented in the 
drawings. The radius defining the respective recesses 12a is larger than 
the corresponding radius defining the semicylindrical bosses 4d. Further, 
as may be seen particularly in FIG. 7, the recesses 12a in the side edges 
of circuit board 12 are offset upwardly from the bosses 4d such that 
engagement between the respective bosses 4d and recesses 12a occurs in the 
lower quadrant of each, thereby urging circuit board 12 downwardly upon 
the crest of the boss 4d engaging the recess 12a in the bottom edge of the 
circuit board. This provides a three-point interference fit for the 
circuit board 12 within the housing chamber 4a. The circuit board 12 may 
be inserted and removed from chamber 4a with only light finger pressure, 
but will remain firmly in place against the shoulders between ribs 4c and 
bosses 4d and against the face of bottom wall 4e while installing and 
removing cover 6. The location of the respective ribs 4c, bosses 4d and 
recesses 12a at the left and right-hand sides of the housing chamber 4a 
and circuit breaker 12, respectively, provide for proper orientation of 
the circuit board 12 relative to the housing 4. As seen in FIG. 7, the rib 
4c, boss 4d and respective recess 12a on the left-hand side of the chamber 
4a are located closer to bottom wall 4e of the chamber than are the 
similar features on the right-hand side of the chamber. Further, no boss 
or recess are provided along the top edge of the chamber and circuit 
board. This arrangement of mounting bosses and recess permits the circuit 
board assembly to be assembled only in one (proper) orientation. 
Circuit board 2 has a pair of wiring terminals 14 mounted thereon 
projecting from a surface exposed to the rear of the sensor assembly. Each 
wiring terminal 14 has a pair of round posts 14a which project through and 
are secured within plated through holes 12b formed in the upper left and 
lower right-hand quadrants of the circuit board 12 as viewed from the back 
in FIG. 7. A central pair of plated through holes 12c receive respective 
pins of a photoelectric sensor device 16 attached to the opposite surface 
of circuit board 12 as wiring terminals 14. As may be seen in FIG. 7, a 
conductive trace 12d connects one of the plated through holes 12c to one 
of the plated through holes 12b directly connecting one pin of the 
photoelectric device 16 to a terminal 14 of the circuit board 12. Circuit 
board 12 is particularly arranged to receive either a photoelectric sensor 
source such as a light emitting diode (LED) 16a (FIGS. 6, 8 and 9) or a 
photoelectric sensor detector such as a phototransistor 16b as seen in 
FIGS. 10 and 11. Each device 16a and 16b has two pin terminals which are 
received in the plated through holes 12c for mounting the device to the 
circuit board 12. The opposite surface of circuit board 12 is provided 
with a pattern of electrically conductive traces as seen in FIGS. 8 and 
10. A pair of resistors R1 and R2 are mounted to the traces by surface 
mount technology for either source or detector application of the circuit 
board 12. 
The source circuit board 12 is shown in FIG. 8 and the schematic diagram 
therefore is shown in FIG. 9. The photoelectric sensor source is the light 
emitting diode 16a connected in series with resistor R2 between positive 
and negative wiring terminals 14. A diode D1 is surface mounted to the 
traces in series with resistor R1 and reversely poled around LED 16a to 
protect the LED in the event the sensor is connected with reverse 
polarity. Diode D1 has three terminals for mounting purposes, but the 
diode is actively connected between only two of the terminals. As viewed 
in FIG. 8, the upper right-hand terminal of diode D1 is not electrically 
active. Three pads 12e, 12f and 12g of the conductive traces are not 
utilized in the circuit board 12 for the photoelectric sensor source. 
The circuit board 12 for the photoelectric sensor detector is shown in FIG. 
10 and the schematic diagram therefor is shown in FIG. 11. The 
photoelectric sensor detector is phototransistor 16b which has its 
collector-emitter connected in series with resistor R2 between the 
positive and negative wiring terminals 14. A transistor Q1 has its 
collector-emitter connected in series with resistor R1 between terminals 
14(+) and 14(-) across phototransistor 16b and resistor R2. The base of 
transistor Q1 is connected to the junction between the emitter of 
phototransistor 16b and resistor R2. A second transistor Q2 has its 
emitter-collector path connected directly in series with terminals 14(+) 
arid 14(-) in shunt of the remainder of the detector circuit. The base of 
transistor Q2 is connected to the junction of resistor R1 and the 
collector of transistor Q1. Transistors Q1 and Q2 are attached to the 
conductive traces of circuit board 12 by surface mount technology, the 
transistor Q2 being attached to the pads 12e, 12f and 12g which were 
unused in the embodiment for the emitter. Transistors Q1 and Q2 provide 
amplification of the signal provided by phototransistor 16b. 
The circuit board assembly is either a source or a detector according to 
the particular components attached thereto. The circuit board is inserted 
into chamber 4a of housing 4 through the open rear side thereof with the 
photoelectric sensor device 16a or 16b facing lens portion 4b of housing 4 
and wiring terminals 14 extending to the rear of the sensor assembly. The 
circuit board is positioned within the housing by its engagement with the 
shoulders on ribs 4c and with face 4e such that the photoelectric device 
is properly located relative to the focal length of the lens. Cover 6 is 
then attached to the housing 4 and the sensor assembly 2 is secured 
together and to a mounting conduit, bar or post by screws 8 and nuts 10 as 
aforedescribed. The photoelectric sensor assembly herein described is used 
in through beam photoelectric sensor applications wherein a sensor 
assembly having a source element is used in cooperation with a second like 
sensor assembly having a detector element. 
A low cost photoelectric sensor assembly is achieved by molding the housing 
of a plastic material having optical qualities, whereby a lens is an 
integrally molded portion of the housing, and by integrally molding 
mounting structure with the housing and the cover. Provision of a circuit 
board common to both a source circuit and a detector circuit reduces the 
cost of the circuit board assembly. Mounting features for the circuit 
board in the housing are incorporated in the housing molding. Finally, 
provision of only three major components for the sensor assembly, i.e. the 
housing, the cover and the circuit board assembly, reduces manufacturing 
stock and assembly time, each of which contribute to reduced cost. Field 
repairability is accomplished by making the circuit board assembly easily 
removable and replaceable. 
The foregoing has described a preferred embodiment and best mode 
contemplated of providing the photoelectric sensor assembly according to 
this invention. However, it is to be understood that the invention is 
susceptible of various modifications without departing from the scope of 
the appended claims. By example, one contemplated alternative embodiment 
is shown in FIG. 12. Housing 4 is essentially the same as aforedescribed 
and is given the number 4'. A particular difference is that housing 4' has 
a cover 4p integrally molded therewith, connected to the main body portion 
of the housing by a living hinge 4q. Cover 4p has a pair of holes 4r for 
the wiring terminals of the circuit board 12, and a rearwardly projecting 
barrier 4s disposed between the holes and therefore between the terminals. 
The lower wall of housing 4' defining the bottom of chamber 4a' is 
extended rearwardly at 4t to provide a ledge against which the bottom edge 
of cover 4p can engage either with a snap fit detent or a press fit to 
hold the cover closed over the circuit board 12. In the modified 
embodiment, a separate clamping member 20 is provided. Member 20 may be 
made of metal or of plastic. In the embodiment shown, a metal clamping 
member 20 has threaded holes 20a for receiving screws 8, thereby 
eliminating separate nuts 10. Moreover, a formed metal strap having 
threaded nuts welded thereto can be used in place of the member 20.