U.S. patent application number 13/875846 was filed with the patent office on 2016-03-24 for lens carrier and optical module for a light curtain and fabrication method.
This patent application is currently assigned to CEDES SAFETY & AUTOMATION AG. The applicant listed for this patent is CEDES SAFETY & AUTOMATION AG. Invention is credited to Guido Baumgartner, Richard Casty, Danilo Dorizzi, Martin Hardegger, Clau Lombriser, Carl Meinherz, Manfred Norbert Stein.
Application Number | 20160085080 13/875846 |
Document ID | / |
Family ID | 46201389 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160085080 |
Kind Code |
A9 |
Meinherz; Carl ; et
al. |
March 24, 2016 |
LENS CARRIER AND OPTICAL MODULE FOR A LIGHT CURTAIN AND FABRICATION
METHOD
Abstract
A lens carrier and an optical module for forming a light curtain
associated with monitoring a protective field. The lens carrier
includes at least one lens for focussing a radiation beam forming
said light curtain and a lens mask having at least one opening for
shaping the radiation beam to have a predetermined aperture. The
lens carrier is formed by overmolding said lens mask with a
transparent material. The optical module has such a lens carrier
and a module body for mounting a radiation transmitter/receiver
carrier that comprises at least one transmitter and/or receiver for
transmitting and/or receiving said radiation.
Inventors: |
Meinherz; Carl; (Malans,
CH) ; Casty; Richard; (Chur, CH) ; Dorizzi;
Danilo; (Chur, CH) ; Hardegger; Martin;
(Sargans, CH) ; Stein; Manfred Norbert;
(Domat/Ems, CH) ; Lombriser; Clau; (Trun, CH)
; Baumgartner; Guido; (Trimmis, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CEDES SAFETY & AUTOMATION AG |
Landquart |
|
CH |
|
|
Assignee: |
CEDES SAFETY & AUTOMATION
AG
Landquart
CH
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130293966 A1 |
November 7, 2013 |
|
|
Family ID: |
46201389 |
Appl. No.: |
13/875846 |
Filed: |
May 2, 2013 |
Current U.S.
Class: |
359/619;
29/428 |
Current CPC
Class: |
G02B 27/0961 20130101;
G01V 8/10 20130101; Y10T 29/49826 20150115 |
International
Class: |
G02B 27/09 20060101
G02B027/09 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2012 |
EP |
EP12166435.3 |
Claims
1. A lens carrier for use in an optical module for a light curtain
monitoring a protective field, said lens carrier comprising: at
least one lens for focusing a radiation beam forming said light
curtain; a lens mask having at least one opening for shaping the
radiation beam to have a predetermined aperture; and wherein said
lens carrier is formed by overmolding said lens mask with a
transparent material.
2. The lens carrier according to claim 1, wherein said lens mask is
fabricated from a stamped metal sheet.
3. The lens carrier according to claim 1, wherein said at least one
lens is a biconvex lens, a plano-convex lens, or a Fresnel
lens.
4. The lens carrier according to claim 1, further comprising at
least one of an optical functional element and a mechanical
functional element.
5. The lens carrier according to claim 1, wherein said transparent
material is further defined as at least one of a
polymethylmethacrylate (PMMA) material and a polycarbonate (PC)
material.
6. An optical module for a light curtain associated with monitoring
a protective field, said optical module comprising: a lens carrier
having at least one lens for focusing a radiation beam associated
with the light curtain and a lens mask that is overmolded with a
transparent material for shaping the radiation beam; and a module
body for mounting a radiation transmitter/receiver carrier that
comprises at least one transmitter and/or receiver for transmitting
and/or receiving said radiation and positionally associated with
the lens carrier.
7. The optical module according to claim 6, wherein said module
body and said lens carrier are fabricated as one integral molded
part.
8. The optical module according to claim 6, wherein said module
body comprises a stabilization element that is integrated into the
module body for enhancing mechanical stability of the module
body.
9. The optical module according to claim 8, wherein said lens mask
and said stabilization element are fabricated from an electrically
conductive material for forming an electromagnetic shielding.
10. The optical module according to claim 6, further comprising an
optical stop element having at least one opening for letting
radiation from/to said at least one radiation transmitter and/or
receiver pass therethrough.
11. The optical module according to claim 6, further comprising a
mechanical fixing means for attaching said radiation
transmitter/receiver carrier.
12. The optical module according to claim 6, further comprising an
optical shielding element for optically shielding a propagation
path associated with the radiation beam between said module body
and said lens carrier.
13. The optical module according to claim 12, wherein said optical
shielding element is fabricated as a part separate from the module
body and the lens carrier.
14. A method for fabricating an optical module, said method
comprising: fabricating a lens carrier having at least one lens for
focusing and at least one lens mask for shaping a radiation beam;
fabricating a module body for mounting a radiation
transmitter/receiver carrier comprising at least one transmitter
and/or receiver for transmitting and/or receiving radiation
associated with the radiation beam; and wherein said module body is
fabricated by at least one of overmolding said lens carrier or said
lens carrier is fabricated by overmolding said module body.
15. The method according to claim 14, wherein fabricating the
module body further comprises: inserting a stabilization element
into a molding tool after the lens carrier has been fabricated and
without removing the lens carrier from said molding tool; and
overmolding said lens carrier and said stabilization element for
forming said optical module.
16. The method according to claim 15, wherein said stabilization
element is formed by stamping and bending a metal sheet.
17. The method according to claim 14, wherein fabricating the lens
carrier further comprises: producing the at least one lens mask by
stamping and bending a metal sheet, said at least one lens mask
having at least one opening for shaping the radiation beam to have
a predetermined aperture; and overmolding said at least one lens
mask, thereby forming the at least one lens to be aligned with the
at least one opening.
18. The method according to claim 14, further comprising
fabricating the module body from a polybutyleneterephtalate (PBT)
material.
19. The method according to claim 14, further comprising:
fabricating an optical shielding element from an opaque material;
and inserting the optical shielding clement between the lens
carrier and the module body such that the optical shielding element
is aligned for optically shielding a propagation path of the
radiation between said module body and said lens carrier.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European Patent
Application No. EP12166435.3 filed on May 2, 2012 and titled "Lens
Carrier And Optical Module For A Light Curtain And Fabrication
Method" and the disclosure of which is incorporated herein.
BACKGROUND
[0002] The present invention relates to industrial light curtains
which monitor a protective or surveillance field and in particular
relates to optical modules that can be used for such a light
curtain.
[0003] Light curtains which are formed by one or more radiation
beams are usually also referred to as light grids or light
barriers.
[0004] Generally, light curtains detect the movement or intrusion
of objects into guarded zones and may provide protection for human
operators who are working with machines or other industrial
equipment. Some light curtain systems are designed to control and
monitor industrial automation processes and are in particular used
for verifying assembly processes, counting objects, confirming an
ejection process, recognize leading edges of transported goods,
recognizing irregular shapes and a lot of other applications,
etc.
[0005] Safety light curtains employing infrared or visible light
beams are used to provide operator safety in a variety of
industrial applications. In particular, the operator protection
around machinery, such as punch presses, guillotines, molding
machines, automatic assembly equipment, coil winding machinery,
robot operation, casting operations and the like can be improved by
using such light curtains. Conventional light curtains typically
employ light emitting diodes (LED) mounting at spaced positions
along a transmitter bar at one side of the guarded zone, and
phototransistors (PT), photodiodes or photo receivers mounted along
a receiver bar at the opposite side of the zone. The LEDs transmit
modulated infrared light beams along separate parallel channels to
the PTs at the receiver bar. If one or more beams are blocked from
penetration by an opaque object, such as the operator's arm, the
control circuit shuts down the machine, prevents the machine from
cycling, or otherwise safeguards the area.
[0006] As mentioned above, such an interruption of the beam can
also be used for counting objects or verifying the entrance of
goods through defined areas.
[0007] Usually, light curtains comprise two optical units, often
called bars, sticks or strips, which are formed as to different
constructional units, one of the optical units having the function
of an emitter and one of a receiver. This dedicated architecture of
an emitter and receiver, however, has several drawbacks, for
instance the fact that the fabrication costs are high, because each
type of optical unit has to be fabricated differently.
Consequently, there exist concepts that use an architecture,
wherein each optical unit has light emitting elements and light
receiving elements at the same time. By providing the optical units
with identical optical modules, which can operate as a receiver as
well as a transmitter, and by additionally providing plug-in units,
which differentiate the particular optical unit in its function as
the emitter with, for instance, a test input, or as the receiver
with, for instance, the output signal switching devices (OSSD), a
particularly cost-effective way of fabricating optical units for a
large scale production can be achieved.
[0008] Such a modular architecture is for instance proposed in the
European patent application EP 11 162 263.5.
[0009] Known optical modules, however, often suffer from the
problem that the alignment of the optical axis for each of the
radiation beams is difficult and that the fabrication of the whole
module is expensive and involves a lot of rejections due to
defects.
[0010] The problem underlying the present invention therefore is to
provide an optical module and a fabrication method, whereby a
particular cost-effective and reliable fabrication and adjustment
of the optical components can be achieved.
SUMMARY OF THE INVENTION
[0011] The present invention provides an improved lens carrier in
an optical module for use in a light curtain. The lens carrier has
at least one lens for focusing a radiation beam forming the light
curtain and a lens mask having at least one opening for shaping the
radiation beam to have a predetermined aperture.
[0012] According to the present invention this lens carrier is
formed by overmolding the lens mask with a transparent material.
Thus, the lens carrier and at least one lens are fabricated as one
integral part. In the case where a plurality of lenses is formed on
the lens carrier, by means of such a simultaneous overmolding step,
all the lenses can be fabricated and aligned with respect to each
other in one tightly toleranced overmolding step.
[0013] Due to the fact that not a plurality of lenses with smaller
geometrical dimensions has to be aligned individually, but a much
larger array of lenses can be aligned simultaneously, the accuracy
and ease of the alignment is significantly improved.
[0014] By forming the lenses and the lens mask as one combined
part, no separate alignment step has to be performed during
assembly with respect to the position of the lens mask relative to
the lenses. Thus, a very high precision can be reached for the lens
mask placement and the assembly of a complete light curtain can be
performed with much better resolution.
[0015] In particular, when fabricating the lens mask from a stamped
metal sheet, improved thermal expansion characteristics of the lens
carrier can be achieved. It could be shown that the thermal
expansion of the composite lens carrier including a metal lens mask
overmolded with a plastic lens material is determined by the
characteristic values of the metal sheet. These values, however,
are compatible with the printed circuit board on the one hand and
surrounding metal profiles on the other hand. Thus, the robustness
and reliability of the assembled optical module can be improved
even for applications in a rough environment with considerable
temperature differences.
[0016] There are several highly advanced techniques for fabricating
lenses by molding techniques and a variety of different lens forms
can be realized on the lens carrier according to the present
invention. In particular, plano-convex or biconvex lenses can be
formed on the lens carrier. However, also a Fresnel lens can be
fabricated which has the advantage of being much thinner than the
plano-convex or biconvex lenses.
[0017] According to a further advantageous embodiment, the lens
carrier according to the present invention can also be provided
with additional optical or mechanical functional elements. These
optical functional elements can for instance be waveguides for
optical indicator means, parts of laser alignment systems or the
like. The mechanical functional elements may for instance comprise
mounting means, additional mechanical features, which allow a
disassembly of the fully mounted optical module from its housing or
the like.
[0018] In any case, the tolerance chain can be kept short and
therefore any additional optical or mechanical features are
directly correlated with the position of the lenses and the lens
mask.
[0019] According to an advantageous embodiment, the transparent
material which forms the lenses comprises polymethylmethacrylate
(PMMA) or polycarbonate (PC). It is appreciated that all other
transparent materials which have the required chemical and physical
characteristics may of course also be used for fabricating a lens
carrier according to the present invention. An overview over
suitable materials can for instance be found in De Schipper, R. et
al: "Kunststoffoptik", Optik & Photonik, Oktober 2006, Nr. 2,
p. 47-49.
[0020] An optical module according to the present invention
comprises an integrally formed lens carrier and a module body for
mounting a radiation transmitter/receiver carrier comprising at
least one transmitter and/or receiver for transmitting and/or
receiving the radiation. In most cases the carrier will be formed
by a printed circuit board (PCB). In particular, the module body
and the lens carrier can be fabricated as one integral molded part.
Thus, very low tolerances between the at least one lens and the
module body can be achieved. This is particularly advantageous
because the module body in most cases will represent the geometric
reference for aligning the optical module during assembly. Thus,
the tolerances between the optical axis of the lens and any
surfaces to which the optical module is mounted, can be kept
low.
[0021] Furthermore, the module body may comprise a stabilization
element which is integrated into the module body. Thus, the
mechanical stability can be enhanced and furthermore, the thermal
expansion can be adapted to the characteristics of the lens
carrier. If a PCB is mounted to the module body, same has a very
similar thermal expansion as the module, which is particularly
important when LED chips are placed on the printed circuit board by
means of a chip-on-board (COB) assembly technique. However, any
other circuit carriers, e. g. Molded Interconnect Device (MID)
carriers, can also be used. Such an MID carrier can firstly be
fabricated together with the module body in the same molding step,
and secondly provides the possibility of fabricating a
three-dimensional circuit carrier structure. Moreover, the module
body itself could be an MID part where the electrically conductive
leads and optoelectronic components are arranged directly on the
module body. In this case, an additional circuit carrier for the
optoelectronic components can be avoided.
[0022] The stabilization element may furthermore form or be a part
of an optical stop element comprising at least one cut-out for
letting pass the radiation from/to the radiation transmitter and/or
receiver. To this end, the stabilization element is preferably
fabricated from an opaque material, for instance from a stamped
metal sheet. In this particular case, when fabricating the
stabilization element as well as the lens mask from an electrically
conductive material, these sheets additionally provide an
electromagnetic shielding for the underlying electronic components
on the PCB. For mounting the printed circuit board on the module
body, same can advantageously be provided with mechanical fixing
means, such as protrusions, snap-in hooks, snap-in notches, or the
like. The dimensions of the cut-outs may also be defined by the
overmolded plastic material in order to form a particularly tightly
toleranced aperture.
[0023] In order to avoid that neighboring radiation paths are
disturbed, the optical module according to the present invention
has an optical shielding element (also called beam separator in the
following), which can be inserted as a part separate from the
module body and the lens carrier. As this part does not need any
particularly accurate alignment, it can be fabricated as a cheap
and simple part, which is preferably formed from an opaque
material.
[0024] A method for fabricating an optical module according to the
present invention includes fabricating a lens carrier by
overmolding a lens mask with a transparent material and providing a
module body, which is fabricated by overmolding the lens carrier.
Thus, both parts can be fabricated within the same tool so that a
particularly accurate alignment and low tolerances can be
achieved.
[0025] According to an advantageous embodiment, first the lens mask
is inserted into the tool which is then overmolded to form the lens
carrier. Without removing the lens carrier from the molding tool in
a next step the stabilization element may be positioned within the
molding tool and the lens carrier and the stabilization element are
then overmolded to form the integrated optical module. This is a
particularly fast, time-saving and at the same time accurate
fabrication method for an optical module according to the present
invention. On the other hand, when the module body and the lens
carrier are formed separately, the beam separator cam be integrated
into the module body or can be mounted in a direction along the
optical axis of the radiation beam.
[0026] Of course, the module body and the lens carrier can also be
fabricated in separate molding steps and subsequently be attached
to each other.
[0027] According to the present invention, the optical shielding
element is preferably inserted after removing the module body with
the lens carrier from the molding tool by sliding in the optical
shielding element in a direction across to the optical axis of the
at least one lens.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings are incorporated into and form a
part of the specification to illustrate several embodiments of the
present invention. These drawings together with the description
serve to explain the principles of the invention. The drawings are
merely for the purpose of illustrating the preferred and
alternative examples of how the invention can be made and used, and
are not to be construed as limiting the invention to only the
illustrated and described embodiments. Furthermore, several aspects
of the embodiments may form--individually or in different
combinations--solutions according to the present invention. Further
features and advantages will become apparent from the following
more particular description of the various embodiments of the
invention, as illustrated in the accompanying drawings, in which
like references refer to like elements, and wherein:
[0029] FIG. 1 shows a perspective view of an optical unit with a
printed circuit board mounted thereto;
[0030] FIG. 2 shows a schematic sectional view of the arrangement
of FIG. 1;
[0031] FIG. 3 shows a lens mask according to a first
embodiment;
[0032] FIG. 4 shows a lens mask according to a second
embodiment;
[0033] FIG. 5 shows a stabilization element;
[0034] FIG. 6 shows a schematic representation of the stabilization
element and the belonging module body;
[0035] FIG. 7 shows a perspective view of the lens carrier and the
module body after removal from the molding tool;
[0036] FIG. 8 shows a perspective view of the optical module after
insertion of the optical shielding element;
[0037] FIG. 9 shows a schematic representation of the various
tolerances for an LED position;
[0038] FIG. 10 a schematic cross-section through a biconvex lens;
and
[0039] FIG. 11 shows a schematic sectional view of a Fresnel lens
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] The present invention will now be explained in more detail
with reference to the figures. In particular, FIG. 1 shows in a
perspective view an optical module 100 according to the present
invention with a printed circuit board (PCB) 102 connected thereto.
The optical module with the PCB 102 are to be mounted in an outer
housing, a so-called profile (not shown in the figures).
[0041] As shown in FIG. 1, the combination of the optical unit 100
and the PCB 102 represents the functional unit for transmitting
and/or receiving light which forms a light curtain for monitoring a
desired surveillance area. A second, corresponding optical module
with a printed circuit board is arranged opposing to the one shown
in FIG. 1. Alternatively, also reflecting elements can of course be
used.
[0042] The PCB 102 carries the light-emitting and/or receiving
elements and the required interconnection leads. If necessary, also
integrated circuitry can be provided on one or both of the surfaces
of the printed circuit board 102. The emitted radiation can in
particular be visible light, in particular red light with a
wavelength range of 620 nm to 750 nm. By using visible light,
optical units containing optical modules according to the present
invention can be aligned when mounting same in the surveillance
area by visual control of a human operator. In contrast to light
curtains where infrared light is used for the emitters, such an
alignment can be performed without additional costs and
furthermore, the eye protection requirements can be fulfilled much
more easily. At the geometric position of each radiation beam the
PCB 102 may carry an LED as a light emitting device or a photodiode
as a light detecting element or may even carry combined transceiver
element, as this is for instance proposed in the European patent
application EP 11 162 263.5 "Modular light curtain and optical unit
for a light curtain".
[0043] According to the present invention, the optical module
comprises a lens carrier 104, which combines a plurality of lenses
106 as one integral unit. A module body 108 serves for mounting the
PCB 102 and furthermore carries a stop element having openings for
letting pass the radiation between the PCB 102 and the lens 106.
This will become more apparent when further looking at FIG. 2.
Mounting and alignment means 112 are provided for adjusting the
position of the optical module with the PCB 102 in a profile (not
shown in the figures).
[0044] As all the lenses 106 of the optical module 100 are
fabricated as one single part, there is no requirement of aligning
same individually when assembling the optical module 100.
Consequently, a very high accuracy regarding the distance and the
parallelism of the radiation beams can be achieved. As this is
generally known for light curtains, different resolution standards
are defined according to the particular application field to be
monitored. A light curtain normally has several beams that are
placed closely together, whereas a light grid consists of only one,
two, three or four light beams. The beams are closest on a light
curtain that is used for finger detection, then the resolution is
commonly 14 mm. Light curtain beams are commonly at their widest
spacing when used for thigh detection (such as at 90 mm
resolution). Accordingly, hand resolution is commonly defined at
approximately 30 mm resolution.
[0045] For separating the individual beams from each other and for
avoiding interference of scattered light, the optical module 100
further comprises a beam separating element 114. The beam
separating element 114 is preferably fabricated from an opaque
plastic material and separates the space between the lens 106 and
the LED or photodiode on the PCB 102 into individual chambers.
[0046] FIG. 2 shows a schematic sectional view of the arrangement
of FIG. 1. On the PCB 102 a light receiving and/or a light emitting
element 116 is mounted. This optical sender and/or receiver 116
defines a first optical axis 118. On the other hand, the centre of
the lens 106 defines a second optical axis 120. These two optical
axes preferably coincide, but in any case are preferably as close
as possible to each other. According to the present invention, the
lens carrier 104 is formed by overmolding a lens mask 122 with a
transparent plastic material. The transparent material may for
instance comprise polymethylmethacrylate (PMMA) or polycarbonate
(PC). The lens mask 122 has openings corresponding to the location
of each lens 106, which are formed to shape the radiation emitted
by a light-emitting element 116 into a particular beam shape
corresponding to the required resolution of the light curtain.
[0047] Moreover, for shaping the transmitted light at the direct
source, an optical stop element 110 with a small opening 124 is
provided. This optical stop element can also be an integral part of
the module body 108. A preferably metallic stabilization element
126 is integrated within the optical stop element 124. The beam
separating element 114 defines different chambers under each lens
106 for optically shielding the individual beams from each
other.
[0048] For fabricating the optical module 100 according to the
present invention, the lens mask 122, which is shown in more detail
in FIGS. 3 and 4, is fabricated from a stamped and bent metal
sheet. The lens mask is aligned in a molding tool and overmolded
with a transparent plastic material to form the lens carrier 104
with a plurality of lenses 106. According to the present invention,
the lens carrier is preferably not removed from the molding tool,
but in a next step, the stabilization element 126, which will be
explained in more detail referring to FIG. 5, is aligned in the
molding tool. In a subsequent second molding step the module body
108 is fabricated. The used material may for instance be
Polybutyleneterephthalate (PBT).
[0049] By fabricating the module body as one integral molded part
with the lens carrier very tight tolerances can be achieved,
because the elements which define the later mounted position of the
PCB 102 are fabricated within the same tool as the lens 106.
According to the embodiment shown in FIG. 2, a plurality of
mounting projections 128 interact with corresponding openings in
the PCB 102 for mounting same at the module body 108.
[0050] However, the module body 108 can also be formed as a
separate component which is joined with the lens carrier 104 by any
known mechanical means.
[0051] A further advantageous feature of the present invention is
the fact that by integrating metal structures as the lens mask 122
and the stabilization element 126, the thermal expansion of the
lens carrier 104 and the optical stop element 124 are much closer
to the thermal expansion of the PCB 102 than a pure plastic
material would be. Consequently, even under significantly differing
temperature conditions, the alignment between the position of the
light receiving and/or emitting elements 116, the openings of the
optical stop element and the optical axes of the lenses 106 can be
achieved.
[0052] A further advantage of using an electrically conductive lens
mask and, in particular, stabilization element 126 is the
additional effect of an electromagnetic shielding towards the PCB
102.
[0053] FIGS. 3 and 4 show two particular embodiments of the lens
mask 122 before same is overmolded with the transparent lens
material. In particular, FIG. 3 shows a form of the masking opening
130, which can be used for optical modules that allow the
application in an environment where a hand resolution is required.
In particular, the light passing through two or more openings 130
is combined to form one radiation beam and a larger distance is
left between one beam and the next. FIG. 4, on the other hand,
shows a lens mask 122 that is suitable for shaping closely adjacent
radiation beams for a finger resolution. To this end, the openings
in the lens mask 130 have the shape of two circular arcs forming an
eye shaped, biconvex outline.
[0054] According to one advantageous embodiment, the lens mask 122
further comprises additional openings and protrusions which can
serve purposes as mounting an alignment laser or indication LEDs or
the like. The lens mask 122 is fabricated by stamping and bending a
metal sheet.
[0055] According to a preferred embodiment of the present
invention, the optical stop element 110, which is formed integrally
with the module body 108, also contains an integrated metal part,
the stabilization element 126 shown in FIG. 5. The stabilization
element 126 is preferably fabricated in a similar process as the
lens mask 122 by stamping and bending a metal sheet. In particular,
for defining small apertures of the optical stop element, cut-outs
124 are provided, which in the finally mounted state correspond to
the positions where the light receiving and/or emitting elements
are located on the printed circuit board 102. In addition to
providing mechanical stabilization in the plane of the optical stop
element 110 of FIGS. 1 and 2, the stabilization element 126 has
reinforcement elements 132 that extend along a sidewall of the
module body for adding mechanical stability thereto. In particular,
the mounting and alignment means 112 can be reinforced by such a
reinforcement element 132. Due to its electrical conductivity, the
stabilization element 126 also provides electromagnetic shielding
for the adjacent PCB components.
[0056] FIG. 6 shows how the plastic material forming the module
body 108 is cast around the stabilization element 126. In this
figure, the lens carrier which may be overmolded together with the
stabilization element 126 in the same fabrication step is not
shown.
[0057] FIG. 7 shows the complete part after overmolding the lens
carrier 104 and stabilization element 126 to form the module body
108. This is the state of the part where it is removed from the
molding tool. In a final step, the beam separating element 114 is
inserted in a direction 134 across to the optical axis of the
lenses 106 (see FIG. 8).
[0058] By fabricating the optical module 100 according to the
fabrication steps explained above, very tight tolerances can be
reached for the position of the LED or photodiode with respect to
the optical axis of the lens. FIG. 9 compares the tolerances of the
chip placement on the PCB 102 and the tolerance of the PCB
placement with respect to the module body 100. With a desired
central position with regard to the openings 124 it can be shown
that in any case the LED 116 is sufficiently centered with respect
to the opening 124. Chip LEDs as well as surface mount technology
(SMT) LEDs can be used in an optical module according to the
present invention.
[0059] Although the overmolded lenses 106 are always shown as being
formed by biconvex lenses in the previous figures and as shown in
FIG. 10, it is not necessarily required to form biconvex lenses.
FIG. 11 shows the alternative structure of a Fresnel lens cast
around the lens mask 122. As can be seen from the direct comparison
with FIG. 10, the advantage of using a Fresnel profile for forming
the lens 106 is the uniform and significantly reduced thickness of
the Fresnel lens. In particular for the molding step, a more
uniform thickness is advantageous. On the other hand, much smaller
sizes of the optical module 100 can be reached with flat lenses
which may be advantageous in tight installation spaces.
Furthermore, also plano-convex lenses can be formed.
[0060] In summary, the present invention provides an improved
optical module for a light curtain by combining or alternatively
using the following improvements:
[0061] The lenses are fabricated with an integrated lens mask by
placing a metal sheet which serves as the lens mask into the
molding tool in a first step and by overmolding this metal sheet
with the lens material, e.g. PC or PMMA. Hence, one single part is
produced instead of a lens and a separate lens mask, thus
facilitating the mounting process. A very high precision can be
reached for the lens mask placement. When using such an assembly
for safety light curtains, a very exact resolution can be achieve
because the lens mask has extremely low tolerances in respect to
the lens. Furthermore, the thermal expansion is defined by the
metal sheet instead of the plastic characteristics and therefore is
much less critical than for pure plastics. Moreover, Fresnel lenses
can be used instead of standard biconvex or plano-convex
lenses.
[0062] A module body according to the present invention is also
preferably reinforced with an integrated metal sheet. Firstly, the
metal sheet is stamped to the required shape and secondly, the
metal sheet is bent as required and placed into a molding tool. In
a third step the metal sheet is overmolded with the module body
material, e.g. PBT. In an advantageous way, the mechanical
stability and robustness of the module body is enhanced by the
metal sheet. Preferably, no glass fibers are needed in the plastic
for improvement of stability, which could impair the mechanic
tolerances. Furthermore, avoiding glass fibers in the plastic
material also extends the lifetime of the molding tool. The thermal
expansion coefficient of a module body having an integrated metal
sheet is very similar to the coefficient of a PCB, resulting in a
very accurate positioning of the optical components with respect to
the module body.
[0063] Finally, the module body and the lens carrier can be
fabricated as one integrated molded part. In a first step the lens
with the lens mask are fabricated by a molding step. In a second
step, in the same tool and without extracting the lens carrier, the
module body is molded so that one single part is formed including
the lens and the module body.
[0064] Hence, very low tolerances between the lenses and the module
body can be achieved. The integrated metal sheets of the lens mask
and the stabilization element equalize the thermal expansion of the
two parts and approximate same to the thermal expansion coefficient
of a PCB. This is particularly important when LED chips, which are
not much bigger than the aperture in front of the LED, are placed
on the PCB by means of a chip-on-board assembly technique.
[0065] Finally, it should be mentioned that the use of the terms
"a" and "an" and "the" and similar referents in the context of
describing the invention (especially in the context of the
following claims) are to be construed to cover both the singular
and the plural, unless otherwise indicated herein or clearly
contradicted by context. The terms "comprising," "having,"
"including," and "containing" are to be construed as open-ended
terms (i.e., meaning "including, but not limited to,") unless
otherwise noted. Recitation of ranges of values herein are merely
intended to serve as a shorthand method of referring individually
to each separate value falling within the range, unless otherwise
indicated herein, and each separate value is incorporated into the
specification as if it were individually recited herein.
[0066] All methods described herein can be performed in any
suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0067] Exemplary embodiments are described herein. Variations of
those embodiments may become apparent to those of ordinary skill in
the art upon reading the foregoing description. The inventor(s)
expect skilled artisans to employ such variations as appropriate,
and the inventor(s) intend for the invention to be practiced
otherwise than as specifically described herein. Accordingly, this
invention includes all modifications and equivalents of the subject
matter recited in the claims appended hereto as permitted by
applicable law. Moreover, any combination of the above-described
elements in all possible variations thereof is encompassed by the
invention unless otherwise indicated herein or otherwise clearly
contradicted by context.
* * * * *