Note: Descriptions are shown in the official language in which they were submitted.
CA 02622170 2008-02-25
CROSS REFERENCE TO RELATED APPLICATIONS
The present patent application is a Continuation-In-Part of copending U. S.
Patent
Application Serial No. 11/096,901, filed April 1, 2005 and entitled "A
FLUORESCENT TASK
LAMP WITH OPTIMIZED BULB ALIGNMENT AND BALLAST."
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention generally relates to handheld electric appliances such
as handheld
fluorescent lighting units having an improved electronic ballast, enhanced
forward illumination,
resistance to mechanical impact, accommodation of one or more of various types
of fluorescent
bulbs, and a pivoting strain relief for a power cord and the like.
2. Description of the Prior Art:
Portable, hand-held drop lights or task lamps utilizing an incandescent bulb
and powered by
AC line current, typically 120 Volts AC, 60 Hz, allow the user to provide
light where installed light
fixtures do not provide adequate coverage. However, incandescent bulbs as the
light source in task
lamps have several disadvantages. It is well known that incandescent light
bulbs are not economical
to operate because much of the electrical energy used by the task light is
converted to heat. The
tungsten filament in a typical 100 Watt incandescent bulb causes the bulb to
get too hot to touch, or
even use close to one's person. Moreover, the relatively fragile nature of the
tungsten filament
impairs the utility of a task lamp in many work situations. One alternative to
the use of
incandescent bulbs is the fluorescent bulb. Fluorescent bulbs convert more of
the supplied electrical
energy to light energy and radiate much less heat than do incandescent lights.
The light emitting
medium in fluorescent lights is a phosphor coating, unlike the thin, fragile
tungsten filament in an
incandescent light bulb. In a fluorescent lamp bulb, a glass tube containing a
small amount of gas -
mercury vapor, for example - is provided with coated cathode electrodes at
either end of the tube.
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CA 02622170 2008-02-25
When a high enough voltage is applied between each pair of electrodes at the
ends of the glass tube,
the coated filament is heated and emits electrons into the gas inside the
tube. The gas becomes
partially ionized and undergoes a phase change to a plasma state. The plasma
is conductive and
permits an electric arc to be established between the electrodes. As current
flows in the plasma,
electrons collide with gas molecules, boosting the electrons to a higher
energy level. This higher
energy level is not a stable condition and when the electron falls back to its
normal energy level, a
photon of ultra-violet light is emitted. The photons in t:urn collide with the
phosphor coating on the
inside of the glass tube, imparting their energy to the phosphor ions, causing
them to glow in the
visible spectrum. Thus the phosphor coating luminesces and gives off the
characteristic
"fluorescent" light. However, fluorescent bulbs require a relatively high
voltage to initiate the
plasma state. After the plasma state is initiated, i.e., the bulb is ignited,
the effective resistance of the
plasma between the electrodes drops due to the negative resistance
characteristic of the fluorescent
bulb. Unless the current is limited after ignition of the bulb, the tube will
draw excessive current and
damage itself and/or the supply circuit. The dual functions of igniting the
fluorescent bulb and
limiting the current in the bulb after ignition takes place are performed by a
ballast circuit. The
ballast for full-sized installed light fixtures includes a large
transformer/inductor, to transi:orm the
supplied line voltage, typically 120 Volts AC available at a wall outlet to a
high enough potential to
ignite the lamp and also to provide a high enough inductive impedance in the
supply circuit: to limit
the current during operation. For typical installed lighting fixtures using
non-self-starting bulbs and
operating at 120 VAC, 60 Hz, the wire gauge, the number of turns in the coils,
and size of the
magnetic core result in a large and heavy ballast component. The ballast
circuits for so-called "self-
starting" fluorescent bulbs are typically smaller, yet still provide an
appropriate voltage to ignite the
lamps without a separate starter. The inductive impedance of the ballast
circuit then regulates the
current draw in a similar manner to that previously described for non-self
starting bulbs.
In recent years electronic ballast circuits have been developed to replace the
large inductors
used in the traditional fluorescent lamp ballasts. The electronic ballasts are
much lighter in weight
because they operate at much higher frequencies and thus have much smaller
inductive components.
Such "solid state" ballasts are also very efficient and can be manufactured at
low cost, making them
especially suited for use in small, handheld fluorescent lamps. In one example
of the prior art, U. S.
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CA 02622170 2008-02-25
Patent No. 6,534,926, Miller et al., a portable fluorescent drop light is
disclosed that contains a pair
of twin-tube compact fluorescent lamp (CFL) bulbs that are individually
switched. The discrete
solid state drive circuit used as a ballast for non-self-starting bulbs
utilizes the CFL bulbs as part of
the oscillating circuit and has a relatively high component count. A different
ballast circuit is
required for use with self-starting bulbs. Miller et al. thus has the
disadvantages of relatively high
component count, and is not capable of driving non-self-starting or self-
starting bulbs from the same
ballast circuit. Further, while the output from the two 13 Watt CFL bulbs
provides adequate
illumination, the diffuse light is radiated into all directions and is not
controlled or directed in any
way so as to maximize the utility of the illumination for task lighting. The
portable fluorescent lamp
disclosed by Miller et al. further appears to lack the ability to withstand
mechanical impacts that
frequently occur during the use of task lamps.
A need exists, therefore, for an economical, portable hand-held task lamp that
provides a light
output substantially equivalent to that of a 100 Watt incandescent bulb, is
efficient to operate, and
does not operate at excessively high temperatures. A need also exists for a
cool-running, efficient
task lamp that provides an enhanced illumination output, directing the
available light toward the task
being illuminated. A need also exists for a ballast circuit design that can
accommodate and operate
with either self-starting or non-self-starting bulbs, can start and run
whether one or both bulbs are
installed in the task lamp, and does not require separate switches or separate
circuits to operate two
or more bulbs. The lamp should further be resistant to damage from mechanical
impact and utilize
inexpensive, readily available fluorescent bulbs. It would be a further
desirable feature to provide as
light-weight and compact a task lamp as possible.
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CA 02622170 2008-02-25
SUMMARY OF THE INVENTION
Accordingly there is provided a handheld fluorescent task lamp comprising a
housing
assembly having a housing and a generally tubular lens body enclosing compact
fluorescent (CFL)
bulbs, an elongated spine configured for slidingly supporting the lens body,
and a resilient bulkhead
for cushioning the CFL bulbs in the lens body; an electronic ballast circuit
within the housing
comprising a power supply, a self-starting electronic driver circuit operable
to start and run at least
first and second CFL bulbs; a bulb accommodation circuit that enables
operation of the electronic
ballast circuit with either starter type or non-starter type and regardless
whether one or both CFL
bulbs are connected to the driver circuit; and an illumination assembly,
wherein the CFL bulbs are
oriented with respect to each other such that an enhanced forward emission
field is provided.
Accordingly there is disclosed an electronic ballast circuit for a handheld
fluorescent task
lamp, comprising a power supply controlled by an ON/OFF switch; a self-
starting electronic driver
circuit operated by the power supply and operable to start and run at least
first and second CFL bulbs
from a single output; first and second receptacles for connecting the first
and second CFL bulbs to
the single output of the driver circuit; and a bulb accommodation circuit in
the electronic driver
circuit that enables operation of the electronic ballast circuit with either
starter or non-starter type
fluorescent bulbs and with either one or both bulbs.
Accordingly there is disclosed an illumination assembly for a handheld
fluorescent task lamp,
comprising first and second elongated compact fluorescent (CFL) bulbs
positioned in an upright
orientation side by side in the task lamp; a self-starting electronic driver
circuit connected to and
operated by a power supply and operable to start and run the at least first
and second CFL bulbs; and
first and second receptacles for connecting the first and second CFL bulbs to
the driver circuit and
orienting the first and second CFL bulbs at a predetermined optimum angle with
respect to each
other such that an enhanced forward emission field is provided.
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CA 02622170 2008-02-25
Accordingly there is disclosed an impact resistant assembly and housing for a
handheld
fluorescent task lamp comprising a housing configured as a hollow tubular
handle; a generally
tubular lens body molded of a substantially clear plastic material, seated in
a recess within an open
first end of the housing and enclosing at least one compact fluorescent (CFL)
bulb; an elongated
spine member extending from a rearward side of the open first end of the
housing and configured for
slidingly supporting the lens body on a track or rail formed along a rearward
portion of the lens body;
and a resilient bulkhead disposed within a distal portion of the lens body and
configured for
supporting and cushioning a distal end of the at least one CFL bulb.
Accordingly there is provided a fluorescent task lamp comprising: a housing
assembled from
first and second shells joined at a parting line and having a first end for
supporting a lens body and
first and second CFL bulb receptacles; a lens body seated upon the first end
of the housing and
enclosing first and second CFL bulbs installed in the first and second CFL
bulb receptacles; and a
strain relief configured upon a first end of an AC power cord having an
integral hub portion and first
and second pivot pins that pivot within first and second opposing pivot
bushings formed respectively
in each first and second shell in opposite sides of an aperture or cavity for
receiving the hub portion
therein disposed in a second end of the housing opposite the first end.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a pictorial perspective view of a fluorescent task lamp
according to one
embodiment of the present invention;
Figure 2 illustrates a cross section view through the light producing portion
of the
embodiment of figure 1;
Figure 3 illustrates a pictorial perspective view of the enhanced forward
emission field and
the spotlight emission field produced by the fluorescent task lamp according
to the embodiment of
Figure 1;
Figure 4A illustrates a plan view of how the enhanced forward emission field
is produced by
the fluorescent task lamp according to the embodiment of Figure 1;
Figure 4B illustrates a plan view showing the distribution of light in the
forward e;mission
field produced by the fluorescent task lamp according to the embodiment of
Figure 1;
Figure 5 illustrates an electrical schematic diagram of one embodiment of the
electronic
ballast circuit employed in the fluorescent task lamp according to the
embodiment of figure 1;
Figure 6 illustrates a pictorial view, partially exploded, of one embodiment
of the assembly
of CFL bulbs and their receptacles as employed in the fluorescent task lamp
according to the
embodiment of figure 1;
Figure 7 illustrates an exploded view of major components of the fluorescent
task lamp
according to the embodiment of Figure 1;
Figure 8 illustrates a pictorial view of separated first and second halves of
one embodiment
of the housing of the fluorescent task lamp according to the embodiment of
Figure 1, wherein the
electronic ballast circuit is installed in the handle portion of one of the
halves of the housing;
Figure 9 illustrates a pictorial view of separated first and second shells of
a housing and
strain relief for an electrical appliance according to an alternate embodiment
of the invention; and
Figure 10 illustrates a side view of a strain relief installed in one shell of
the housing of the
embodiment of Figure 9.
~g.,
CA 02622170 2008-02-25
DETAILED DESCRIPTION OF THE INVENTION
In the following description, structures bearing the same reference numbers in
the various
figures are alike. Referring to Figure 1 there is illustrated a pictorial
perspective view of a
fluorescent task lamp 10 according to one embodiment of the present invention,
as viewed from a
perspective above and to the left side of the task lamp 10. The illustrative
task lamp 10 is designed
to be conveniently held in a user's hand or supported by built-in, adjustable
hooks., and is
approximately 13 inches in length, excluding the extendable hooks and the line
cord. The task lamp
includes a housing 12, a clear lens body 14, an elongated spine 16 extending
upward from the
open end of the housing 12, and a flexible cap 18 that fits over the
combination of the upper, closed
end 20 of the lens body 14 and the distal end 17 of the elongated spine 16.
The distal end 17 of the
elongated spine 16 is barely visible in Figure 1 through the closed end 20,
but see also Figures 7 and
8. Further, the close observer will note that the elongated spine 16 is
disposed relative to the housing
12 at an inclination angle of approximately nine (9) degrees between the
longitudinal axes of the
housing 12 and the elongated spine 16. This inclination angle maybe selected
as a nominal forward-
leaning angle for task illumination when the task lamp is placed in an upright
position on a work
surface. Other inclination angles, generally in the range of zero to twenty
degrees may, of course, be
used. The inclination angle of the illustrative embodiment described herein is
also clearly shown in
Figure 8.
The housing 12 of the fluorescent task lamp 10 is generally tubular, being
hollow to
accommodate electronic circuitry as will be described. The lens body 14 is
supported within the
open end 15 of the housing 12. Enclosed within the clear lens body 14 are
first 22 and second 24
compact fluorescent lamp (CFL) bulbs, supported in a receptacle to be
described herein below. The
first and second CFL bulbs 22, 24 are supported at their upper ends within
openings cut tlirough a
soft, resilient bulkhead 26 to provide resistance to mechanical shock or
impact. A reflector 30,
disposed behind the first and second CFL bulbs 22, 24, is attached to a bulb
side surface of a
reflector panel 58 (See Figure 2). The reflector pane158 may be an integral
part of the lens body 14
or a separate structure installed therein. The reflector 30 is configured to
reflect light emitted by the
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CA 02622170 2008-02-25
first and second CFL bulbs 22, 24 in a forward direction to augment the
forward emission of light
from the first and second CFL bulbs 22, 24. It will also be noted that the
first and second CFL bulbs
22, 24 are oriented at an angle with respect to each other. Positioning the
first and second CFL bulbs
22, 24 such they are turned slightly inward toward each other provides as an
unexpected benefit a
much enhanced forward emission field as will be described in detail herein
below.
Continuing with Figure 1, the housing 12 includes a finger grip 32 having a
plurality of finger
recesses formed in a frontward portion thereof. At the lower end of the
housing 12 is formed an
integral stand or base 34 for use when it is desired to stand the task lamp 10
in an upright position.
The base 34, as will be shown in a subsequent figure, is generally flat to
facilitate the upright
position of the task lamp 10. A three terminal AC outlet 36 or "tool tap" is
provided in the lower
portion of the housing 12 for connecting AC operated tools or other devices.
Alternate embodiments
may utilize a two terminal AC outlet for use with two-wire AC circuits,
although three-wire outlets
are preferred for safety reasons. Power is supplied to the task lamp 10 by the
line cord 38 that is
supported in the lower, rear portion of the housing 12 by a strain relief 40.
The cord may preferably
be a three wire cord having line, neutral and ground conductors, although that
is not essential for the
present invention. As will be explained, the strain relief 40 is formed of
pliable material and the
entire strain relief pivots about a fixed point in the housing 12.
In an upper portion of the rear of the housing 12 a pair of spring wire hooks
46 are provided
to support the task lamp 10 in variety of positions during use. The hooks 46
are attached to the upper
end of a rod 42, which slides upward and downward within a rearward portion of
the elongated spine
16 and extends through the cap 18. The lower end (not shown) of the rod 42
includes an expanded
portion or knob that resists movement within the rearward portion of the cap
18, to facilitate
retaining the hooks 46 in an adjusted position. The hooks 46 may be fabricated
of metal spring wire
and equipped with nylon tips 48 to prevent marring of a surface upon which the
hooks 46 are placed.
The wire gauge selected can be used to advantage. For example, if a smaller
gauge, such as 20
gauge is selected, one or both of the wire hooks 46 may be bent to enable
hanging the task lamp 10
from the edge of a flat surface, for example. The nylon tips 48 prevent the
flat surface from being
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CA 02622170 2008-02-25
marred. Although a larger gauge, such as 18 gauge or 16 gauge spring wire may
be used, the hooks
46 are not as easily bent to provide this increased utility available when a
smaller gauge spring wire
is used.
Several materials are recommended for the structures in the fluorescent task
lamp of the
present invention. The housing 12 is preferably molded of a polypropylene
formulated to provide a
slight amount of resilience to better distribute the shock of impact as when
the task lamp 10 is
dropped. In one embodiment, the elongated spine 16 and the housing 12 are
molded as a single
integrated component, configured as mirror halves to each other. This
integrated construction
provides strength to the combined structures and improved distribution of
impact forces throughout
the housing component. The polypropylene material is also available in a
variety of colors. For
example, the illustrated embodiment may be yellow or orange for safety
recognition, or produced in
any of a variety of other colors. The clear lens body 14, which completely
surrounds the first and
second CFL bulbs 22, 24 (See, e.g., Figure 7 infra), is preferably molded of
glycol-modified
polyethylene terephthalate (PETG) or polyvinyl chloride (PVC). These materials
are very tough and
provide good optical properties as well. The cap 18, which functions as a
"bumper" when the task
lamp 10 is dropped or bumped against another object, may be molded of vinyl
rubber, selected for
the characteristics of flexibility and resilience. As will be described in
figure 7, the inside surfaces of
the cap 18 include small rib-like features that retain the cap in place when
pressed over the
combination of the lens body 14 and the elongated spine 16. The resilience of
the cap 18, as noted
above, also provides some resistance to mechanical shock.
Another mechanical impact resisting component shown in Figure 1 is the soft,
resilient
bulkhead 26, which is visible in the drawing just inside the upper end of the
clear lens body 14. This
bulkhead may be molded of a plastic material or of a mixture of plastics
processed from recycled
polymer residues of various molding operations. It should be a moldable,
resilient material having
approximately a 20 Shore A durometer specification, within a range of +/- 10
Shore A dui-ometer.
The durometer specification selected depends on the expected impact forces and
the dimensions of
the bulkhead itself and the configuration of the bulkhead, i.e., whether
openings or voids are
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CA 02622170 2008-02-25
included in or distributed within the body of the bulkhead. The result of the
above combination of
features and materials provides an impact absorbing housing design that
resists damage to both the
task lamp and the relatively fragile fluorescent bulbs contained within the
lamp caused by
mechanical shock. The total effect of the design of and the materials selected
for the entire housing
assembly of the task lamp 10, including the housing 12, the lens body 14, the
elongated spine 16, the
cap 18 and the flexible bulkhead 26 is to enable the task lamp of the present
invention to withstand
repeated drops from a distance of up to six feet without bulb breakage.
The post 42 (only the upper end of the post 42 is visible in Figure 1) that
supports the hooks
46 may be formed of polypropylene, while the protective tips 48 may be formed
of nylon. The hooks
46 themselves may be formed of 20 gauge steel spring wire. The strain relief
40 may be molded of
PVC. The flexibility of the strain relief is provided primarily by its ribbed
profile. The reflector 30
may be fabricated of aluminized mylar applied to a paper backing and attached
to the bulb-side
surface of the reflector panel 58 using an adhesive (not shown) or one or more
strips of double-sided
tape (also not shown). In the illustrated embodiment, the receptacles for
supporting the first and
second CFL bulbs 22, 24, as will be described infra, are combined into a
single body molded of
polychloride, selected for its strength and insulating qualities.
Referring to Figure 2 there is illustrated a cross section view through the
light producing
portion of the embodiment of figure 1, as viewed in an upward direction toward
the cap 18. Shown
in Figure 2 are the lens body 14, the elongated spine 16, and the reflector
30, all shown in cross
section. Also visible in Figure 2 is the relationship between the elongated
spine 16 and the lens body
14, which are nested together. The lens body 14 includes a reflector panel 58,
which includes first
and second tracks or rails 55, 57 that slide along first and second grooves
54, 56 formed in the edges
of the elongated spine 16. The elongated spine 16 further includes a hollow
interior 50, which may
accommodate electrical circuitry or support an additional light source such as
a point source light
emitting diode (LED). Other uses of the hollow interior space 50 are described
in the detailed
description of Figure 8 infra. Beyond and upward from the cross section (into
the plane of the page)
are shown the resilient bulkhead 26, the cap 18, and the hooks 46. The lower
end of the hook post
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CA 02622170 2008-02-25
42 is shown, which slides or rotates within a bore formed in the cap 18. The
first and second CFL
bulbs 22, 24 are shown in cross section.
It will be appreciated that the first and second CFL bulbs 22, 24 are so-
called "twin tube"
bulbs in the illustrated embodiment. The first and second CFL bulbs, in the
embodiment shown may
preferably be 9 Watt rated, have a color temperature of 6500 degrees K., and
are provided with a
GX23 bi-pin base, wherein both ends of the CFL bulb tube are terminated in a
single base structure
that is configured to be conveniently plugged into a receptacle. Other color
temperatures may be
used without changing the advantages provided by the present invention. Other
bases than the GX23
may, of course be used, as long as they permit the bulb alignments required by
the configuration
disclosed herein. As will be further be appreciated from Figure 7, to be
described, the lens body 14
is configured with a slight taper, having a smaller cross section toward the
upper, closed end of the
lens body 14. Further, the resilient bulkhead 26 may include several openings
52 to modify the
resiliency or to conserve material. In the view provided by Figure 2, the
resilient bulkhead 26 is
pushed into a position near the upper, inside, closed end of the lens body 14.
The resilient bulkhead
26 is intended to be positioned where its cross section substantially matches
that of the inside of the
lens body 14. Another purpose of the resilient bulkhead 26 is to maintain the
first and second CFL
bulbs 22, 24 in the correct alignment and spacing to ensure production of the
enhanced forward
emission field.
Referring to Figure 3 there is illustrated a pictorial perspective view of the
enhanced forward
emission field and the spotlight emission field produced by the fluorescent
task lamp according to
the embodiment of Figure 1. Visible in the illustration are the housing 12 of
the task lamp 10,
having a base 34 and a cap 18 as previously described. Projecting principally
into the forward
direction, and partially to either side, is the main portion of the forward
emission field 60 of the light
output from the diffuse fluorescent source within the lens body 14 of the task
lamp 10. Also shown
is a spotlight emission field - substantially beam like - emitted from the end
of the task lamp through
the opening in the cap 18. The emission fields 60, 70 are somewhat idealized
to demonstrate the
" 13'"
CA 02622170 2008-02-25
effects of the novel configuration of components incorporated into the design
of the task lamp of the
illustrative embodiment.
Referring to Figure 4A there is illustrated a plan view of how the enhanced
forward emission
field is produced by the fluorescent task lamp according to the embodiment of
Figure 1. The view is
as if one were looking down at the top of the task lamp with the cap 18, the
resilient bulkhead 26 and
the lens body 14 removed, exposing the upper ends of the first and second CFL
bulbs 22, 24. The
first and second CFL bulbs 22, 24, and the reflector 30 are shown, along with
a first reference point
78 located in the center of the reflecting surface of the reflector 30. The
first reference point 78 is
also on a line that extends forward from and is normal to the reflector 30 at
the first reference point
78. This line is a line of symmetry that bisects the forward emission field
produced by the first and
second CFL bulbs 22, 24, one bulb on each side of and equally spaced from and
oriented identically
with this line of symmetry. This line of symmetry is called the centerline 84
of the forward emission
field, alternately called the FEF centerline 84, and is shown by a broken line
in Figure 4A.,
Continuing with Figure 4A, a reference plane 86 is defined that is normal to
both the FEF
centerline 84 and the plane of the drawing. The reference plane 86 is thus
approximately parallel to
the plane of the reflector 30 at the first reference point 78. The FEF
centerline 84 intersects the
reference plane 86 at a second reference point 79. The first CFL bulb 22 is
shown positioned to the
left of the FEF centerline 84, with the twin tubes of the first CFL bulb 22
aligned at an angle 100
with respect to the reference plane 86. This angle is preferably approximately
13.5 degrees, which is
also the angle of the first plane 88 with respect to the reference plane 86. A
"bulb one" centerline 80
is shown normal to the first plane 88 and extending forward into the forward
emission field 60,
crossing the FEF centerline 84 at a third reference point 85 at an angle equal
to the angle 100 of
approximately 13.5 degrees. Similarly, The second CFL bulb 24 is shown
positioned to the right of
the FEF centerline 84, with the twin tubes of the second CFL bulb 24 aligned
at an angle 102 with
respect to the reference plane 86. This angle is also preferably approximately
13.5 degrees, which is
also the angle of the second plane 90 with respect to the reference plane 86.
A "bulb two" centerline
82 is shown normal to the first plane 88 and extending forward into the
forward emission field 60,
" 14'"
CA 02622170 2008-02-25
crossing the FEF centerline 84 at the third reference point 85 at an angle
equal to the angle 102 of
approximately 13.5 degrees. The alignment angle 92 between the bulb one
centerline 80 and the
bulb two centerline 82 is approximately 27 degrees. It will also be understood
that the angle between
the first and second CFL bulbs, which is the forward angle between the first
plane 88 and the second
plane 90, is approximately 180 - 27 = 153 degrees.
This arrangement of the first 22 and second 24 twin tube CFL bulbs with
respect to the
reflector 30 has been found to yield unexpected and optimum results for
producing a maximum
forward emission field from a pair of CFL bulbs. It is well known that a
fluorescent bulb emits a
diffuse light that is difficult to control or concentrate directionally. In
spite of the use of reflectors,
the light is still very diffuse. However, the arrangement detailed above and
illustrated in Figure 4A
is found to produce a maximum forward emission field that is particularly well
adapted to work light
or task light applications. The forward emission filed 60 concentrates most of
the light emitted from
the first and second CFL bulbs 22, 24 within an angle bounded by the first
boundary 96 and the
second boundary 98. The first and second boundaries 96, 98 represent boundary
planes that are
normal to the plane of the drawing and intersect at the reference point 78 on
the reflecting surface of
the reflector 30 at an emission angle 94 of approximately 108 degrees. This
emission angle 94,
which corresponds to the effective beam width of the forward emission field
60, is bisected by the
FEF centerline 84. Moreover, the emission angle 94, which is approximately 108
degrees, is an
integral multiple of the alignment angle 92 between the first and second CFL
bulb centerlines 80, 82,
which is approximately 27 degrees. To say it another way, the alignment angle
92 between the CFL
bulb centerlines 80, 82 is approximately equal to one quarter of the beam
width (i.e., the emission
angle 94) of the forward emission field 60. This empirical relationship
enables designers of
illumination products to optimize the emission of light from diffuse sources
while also maximizing
the energy efficiency of the lighting apparatus employed to produce the
emission field.
In the foregoing description of Figure 4A, the reflector 30 is shown having a
profile that is
cylindrical, about a longitudinal axis that is substantially parallel to the
longitudinal axes of the first
and second CFL bulbs 22, 24, and has a proportionately large cylindrical or
circular radius of
CA 02622170 2008-02-25
curvature. In some applications, including the illustrative embodiment, this
radius of curvature is
very large, resulting in a reflector 30 that is nearly or substantially flat.
However, the curvature of
the reflector 30 may be concave or convex with respect to the forward emission
field 60 and may be
formed to a variety of shapes including circles or spheres, conic sections, or
faceted profiles. A
faceted reflector may be formed from a plurality of small reflecting elements
to achieve a particular
reflection profile or characteristic suited to a particular application. In
general, the choice of profile
will depend strongly on the spacings between the CFL bulbs and between the CFL
bulbs and the
reflector. The reflector 30 has less effect on the forward emission field in
the illustrated embodiment
because it quite close to the first and second CFL bulbs 22, 24. It will be
observed by the careful
reader that a substantial portion of the light reflected from a closely spaced
reflector, as illustrated in
Figure 4A, is blocked from the forward emission field by the bulbs themselves
because of their close
spacing and their closeness to the reflector.
Referring to Figure 4B there is illustrated a plan view showing the polar
distribution of light
in the forward emission field produced by the fluorescent task lamp according
to the embodiment of
Figures 1 and 4A, wherein the first and second CFL bulbs 22, 24 are disposed
at an angle such that
their respective centerlines 80, 82 intersect at an angle of approximately 27
degrees, according to the
"quarter beam width" principle described in the description of Figure 4A. The
distribution is shown
for useful radii for a handheld task light, that is, for distances of zero up
to four or five meters from
the task lamp, with the most useful illumination occurring within the zero-to-
three meter range. The
drawing includes radii of one, two and three meters for reference. The
perspective is similar to that
of Figure 4A, including the first reference point 78, the FEF centerline 84,
and the CFL bulb one 80
and CFL bulb two 82 centerlines. The disposition of the first and second CFL
bulbs 22, 24 at the
quarter beam width angle of their centerlines and the use of a nearly flat or
only slightly curved
nearby reflector 30 behind them, while it optimizes or enhances the forward
emission field 60, also
produces regions within the forward emission field having varying intensities
of illumination. This
characteristic is illustrated in Figure 4B, and represents the additive
illumination intensities in the
various regions as compared with a pair of twin tube CFL bulbs of the same
wattage rating spaced at
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CA 02622170 2008-02-25
the same distance side-by-side, but aligned, as in conventional fluorescent
task lamps, in a straight
line so that their respective centerlines are parallel.
For example, there are three overlapping forward emission fields illustrated
in Figure 4B. In
addition to the first forward emission field 60 that is defined and shown in
Figure 4B, i.e., that
reaches out to well beyond three meters, there are a second forward emission
field (FEF) 62 and a
third FEF 64. Regions within these FEFs 60, 62, and 64 are identified with
reference numbers.
Regions 110, 112, and 114 are defined for the space within the FEF that lies
between the planes
corresponding to the CFL "bulb one" 80 and CFL "bulb two" centerlines.
Similarly, regions 116,
118, and 120 are defined for the space to the right (in the drawing) of the
CFL "bulb one" centerline
80, and regions 122, 124, and 126 are defined for the space to the left (in
the drawing) of the CFL
"bulb two" centerline 82. Within these regions identified with the reference
numbers are integers
that convey illumination intensity values relative to the value of a pair of
twin tube CFL bulbs
aligned in a straight-line, side-by-side relationship and emitting light into
the space around it. The
intensity values are expressed in the percentage gain in the luminous flux of
the angular alignment of
the two twin tube CFL bulbs as described herein as compared with the straight
alignment
configuration of conventional fluorescent task lamps.
Thus, in region 110, the relative improvement within one meter is + 8%, within
two meters is
+ 4%, and within three meters is +2%. Similarly, in regions 116 and 122, the
relative improvement
within one meter is +4% and within two meters is +2%. The effects are
cumulative throughout the
entire forward emission field 60, and together sum to approximately 33 percent
more illurnination
into the forward emission field than is provided by the conventional straight,
side-by-side al.ignment
of the twin tube CFL bulbs.
To appreciate the enhanced illumination into the forward emission field
provided by the
angular alignment of the first and second CFL bulbs of the present invention,
consider the following
comparison. These two 9 Watt CFL bulbs, in the configuration described in
detail in the illustrated
embodiment, nominally provide an 18 Watt fluorescent task lamp having an
effective liglit output
17
CA 02622170 2008-02-25
that approaches that of a 100 Watt incandescent task lamp. To see why, recall
that in conventional
fluorescent task lamps, two 13 Watt fluorescent bulbs are required to produce
a light output
approximately equivalent to a 100 Watt incandescent bulb, a standard
comparison. This
improvement can be represented by the factor obtained by dividing 100 Watts by
26 Watts, or, about
3.84. Now, multiply this factor 3.84 by 18 Watts, which yields a result of 69
Watts, the equivalent
light produced by a pair of 9 Watt twin tube CFL bulbs arranged in a straight,
side--by-side
alignment, as found in conventional fluorescent task lamps. However, by re-
aligning the two 9 Watt,
twin tube CFL bulbs as in the present invention, a 69 Watt equivalent output
increased by the 33%
improvement described in the preceding paragraph becomes a 92 Watt equivalent
illuniination
output. In other words, the forward emission field has been enhanced by 33
percent. This output is
only eight percent below the "100 Watts" touted for the conventional 26 Watt
fluorescent task lamp.
Of course, this has been a comparison of electrical power required - the power
ratings of the CFL
bulbs - but the comparison is valid because the light outputs are proportional
to the input power
required, all other things being equal.
Referring to Figure 5 there is illustrated an electrical schematic diagram of
one embodiment
of the electronic ballast circuit employed in the fluorescent task lamp
according to the embodiment
of figure 1. The electronic ballast circuit 150 includes three functional
sections, a power supply 152,
a self starting electronic driver circuit 154, and a bulb accommodation
circuit 156. The first and
second CFL bulbs 22, 24 are connected to the bulb accommodation circuit 156
via the first and
second receptacles 158 and 160. As will be described, the ballast circuit 150
operates at least two
CFL bulbs in parallel from a ballast circuit controlled by a single switch,
will start either starter-type
or non-starter-type CFL bulbs, will operate with either one of the bulbs
removed from the circuit, and
will safely discontinue operation with the switch turned ON and either or both
bulbs are removed
from the circuit. The ballast circuit has a very low component count for low
cost and minimum
space requirements and is very efficient, resulting in minimum heat
dissipation. Low heat
dissipation is an important design constraint for electronic circuitry
operating within a small,
enclosed volume as in the housing 12 of the illustrative task lamp 10.
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CA 02622170 2008-02-25
Continuing with the ballast circuit 150, a "line" power line conductor 162
connects via an
ON/OFF switch 164 to a node 166 and further to a line side terminal of an AC
receptacle or outlet
36. A "neutral" power line conductor 168 connects to a node 170 and further to
a neutral side
terminal of the AC receptacle or outlet 36. A ground line conductor 165
connects to a ground
terminal of the AC receptacle or outlet 36. A diode rectifier 172 is connected
between the node 166
(anode) and a node 174 (cathode). The node 174 is further identified as the
positive DC supply
voltage line or rail. A second diode rectifier 176 is connected between the
node 166 (cathode) and a
node 178 (anode). The node 178 is further identified as the negative DC supply
voltage line or rail.
Neither node 174 or 178 is connected to the ground line 165. A first filter
capacitor 180 is connected
between the nodes 174 and 170. A second filter capacitor 182 is connected
between the ncides 170
and 178. The circuit configuration illustrated is a voltage doubler power
supply 152, well known to
persons skilled in the art. The nominal AC voltage input applied across the
Line terminal 162 and
Neutral terminal 168 is 120 Volts AC, 50/60 Hz. The nominal DC output voltage
provided from the
illustrative voltage doubler power supply 152 is approximately 320 Volts DC.
The self starting electronic driver circuit 154 shown in Figure 5 will now be
described.
Connected between the nodes 174 and 178 are a resistor 184, a node 186 and a
capacitor 188.
Another resistor 190 is connected between the node 174 and a node 192. A diode
194 is connected
between the nodes 192 (cathode) and 186 (anode). A first snubber diode 196 is
connected between
the node 174 (cathode) and 192 (anode). A second snubber diode 198 is
connected between the node
192(cathode) and the node 178 (anode). A first NPN transistor 204 and a second
NPN transistor
208 are connected in totem pole fashion between the nod 174 and the node 178.
The collector of
transistor 204 is connected to the node 174 and the emitter of transistor 204
is connected through a
resistor 206 to the node 192 and the collector of transistor 208. The emitter
of transistor 208 is
connected through a resistor 210 to the node 178. The base of transistor 204
is connected through a
resistor 212 and a three turn winding 222B to the node 192, with the polarity
mark of the winding
222B connected to the node 192. The base of transistor 208 is connected
through a resistor 216 and
another three turn winding 222C to the node 178, with the polarity mark of the
winding 222C
connected to the resistor 216. The connection of the resistor 216 and the
marked end of the winding
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CA 02622170 2008-02-25
222C define a node 202. The windings 222B and 222C are two of the three
windings of' a pulse
transformer 222, wound on a toroid core. The node 202 is connected to the node
186 through a
bilateral diode 200. The bilateral diode 200, in the illustrated embodiment,
may be a type 13T-32A
available from Teccor Electronics Inc., Irving, Texas, or its equivalent. The
bilateral diode 200 is
rated at a nominal break-over voltage of 32 Volts and a maximum trigger
current of 2 Amperes. The
node 192 is a common node for the electronic driver circuit 154. Connected
between the node 174
and the common node 192 is a capacitor 220. The third winding 222A of the
pulse transformer 222
is connected between the common node 192 and an output node 224, with the
polarity mark
connected to the node 224.
The output of the electronic drive circuit 154 is a square wave operating at a
frequency of
approximately 32 KHz and a peak amplitude of approximately the 320 Volt rail-
to-rail voltage
produced by the voltage doubler power supply 152. When power is first applied
to the circuit 154,
the capacitor 188 charges through the resistor 184 until it exceeds the break-
over potential of the
bilateral "trigger" diode 200. Capacitor 188 then discharges through the
bilateral diode 200 and
resistor 216, driving the second NPN transistor 208 into saturation and
pulling the common node 192
to very near the negative rail 178. The initial current for transistor 208 is
supplied through capacitor
220. Once started, positive feedback via the transformer 222 windings in the
respective base drive
circuits of the first and second transistors 204, 208 alternately biases the
respective transistor into and
out of saturation, such that one transistor is conducting at a time, and
allows the circuit to oscillate at
a frequency determined by the characteristics of the load, to be described
infra. Thus, once under
way, the alternating current through the transformer winding 222A alternately
biases the first 204
and the second 208 transistor into saturation until the polarity of the
instantaneous voltage appearing
at the common node 192 causes the respective transistor to come out of
saturation. The diode 194
prevents the charge on capacitor 188 from exceeding the break-over potential
of the bilateral diode
200 once the circuit has started. The resistor 190 acts as a bleeder resistor
to discharge the capacitor
220 when power is removed from the circuit. The snubber diodes 196, 198
respectively protect the
transistors 204, 208 from excessive reverse voltages that may occur in the
circuit.
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CA 02622170 2008-02-25
The bulb accommodation circuits 156 shown in Figure 5 will now be described.
It should be
noted in the following description that the first and second CFL bulbs 22, 24
are also designated as
the first and second CFL bulbs 260, 262, and may also be designated as CFL
"bulb one" or CFL
"bulb two." As mentioned in the preceding paragraph, the operating frequency
of the electronic
driver circuit 154 is determined by the characteristics of the load. The load
in the illustrative
embodiment includes the first and second CFL bulbs 260, 262 and their
respective portions of the
bulb accommodation circuit. The two CFL bulb accommodation circuit portions
(hereinafter,
circuits) are connected in parallel between the output node 224 of the
electronic drive circuit and the
positive rail 174 of the supply voltage and each CFL bulb circuit is identical
within the normal
tolerances of the components utilized. Both CFL bulb accommodation circuits
operate the same way
and at the same time. Further, each CFL bulb accommodation circuit may operate
independently;
that is, either bulb accommodation circuit may operate alone or together with
the other bulb
accommodation circuit. Moreover, three or more such bulb accommodation
circuits may be driven
together by the electronic driver circuit as long as the current capability of
the electronic driver
circuit is sufficiently scaled to provide the necessary current.
In the bulb accommodation circuit 156 of "bulb one" 260, an inductor 230 is
connected
between the node 224 and a node 232. A capacitor 242 is connected between the
node 174 and a
node 238. Connected in series between the node 232 and node 238 are, in turn,
a SPST switch 272, a
capacitor 274 and a resettable fuse 276. Also connected between the nodes 232
and 238 are the first
250 and second 252 terminals of a first CFL bulb receptacle 158. Connected to
the first 250 and
second 252 terminals of the first receptacle 158 are the first and second
terminals 262, 264 of the
first CFL bulb (also denoted "bulb one") 260. When the first CFL bulb 260 is
connected to the first
receptacle 158, the normally open contacts of switch 272 close. When the first
CFL bulb is removed
from the first receptacle 158, the contacts of the switch open the series
circuit connected between the
first and second terminals of the first receptacle 158.
Similarly, in the bulb accommodation circuit 156 of "bulb two" 266, an
inductor 234 is
connected between the node 224 and a node 236. A capacitor 244 is connected
between the node
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CA 02622170 2008-02-25
174 and a node 240. Connected in series between the node 236 and node 240 are,
in turn, a SPST
switch 278, a capacitor 280 and a resettable fuse 282. Also connected between
the nodes 236 and
240 are the first 256 and second 254 terminals of a second CFL bulb receptacle
160. Connected to
the first 256 and second 254 terminals of the second receptacle 160 are the
first and second terminals
268, 270 of the second CFL bulb (also denoted "bulb two") 266. When the second
CFL bulb 266 is
connected to the second receptacle 160, the normally open contacts of switch
278 close. When the
second CFL bulb is removed from the second receptacle 160, the contacts of the
switch open the
series circuit connected between the first and second terminals of the second
receptacle 160.
In the illustrative embodiment, the value of the inductors, 230, 234 is
approximately 6.7
milliHenrys. The value of the blocking capacitors 242, 244 is approximately
0.022 uF. The value of
the bypass capacitors 274,280 is approximately 0.0015 uF. Further, the SPST,
normally open switch
272, 278 may be a micro switch mounted just below the receptacles 158, 160.
Alternately, the
switches 272, 278 may be especially formed of beryllium-copper spring stock
and configured for
being mounted within the body of the receptacles 158, 160.
The bulb accommodation circuits 156 are configured to accommodate the
characteristics of
both non-starter type CFL bulbs and starter type CFL bulbs. As is well known,
non-starter type CFL
bulbs contain an internal circuit connected between the two pins (terminals T1
and T2) in the base
of the bulb. From one pin to the other is connected, in turn, a resistive
filament (somewhat like a
heater), a capacitor having a nominal value of approximately 3.0 nF (i.e., 3.0
nanoFarads or 0.003
microFarads or 0.003 uF), and another filament. Starter type CFL bulbs are
similar except that they
include a small neon lamp connected in parallel with the 3.0 nF capacitor
inside the base of the CFL
bulb.
Starting of the electronic ballast circuit 150 operates as follows. Since both
bulb
accommodation circuits 156 are the same, and they are started and driven by a
single self starting
electronic driver circuit 154, they are started by the same mechanism.
Therefore the starting
operation (which applies to either or both CFL bulb 260 and CFL bulb 262) for
the first CFL bulb
"22'"
CA 02622170 2008-02-25
will be described. A non-starter CFL bulb 260 is started or "fired" by the
resonant circuit formed by
the inductor 230 and the internal capacitance of the first CFL bulb 260 (in
combination with the
blocking capacitor 242 and the bypass capacitor 274, though the effect of
these capacitors, because
of their values, is to reduce the operating frequency only slightly - on the
order of approximately 10
percent), which presents a series resonant load to the output of the
electronic driver circuit 1:54. The
series resonant load is a very low impedance, and draws maximum current. As
the circuit oscillates,
in resonance, the voltage across the internal bulb capacitance increases until
the firing voltage of the
bulb is reached (approximately 250 to 300 Volts AC). After the bulb fires, the
forward voltage drop
across the bulb is maintained by the bulb characteristics at approximately 60
to 70 Volts AC, while
the current through the bulb is limited by the inductive reactance of the
inductor 230.
A starter type CFL bulb operates differently. Since the starter type CFL bulb
includes a neon
lamp inside the base of the bulb and connected in parallel with the internal
capacitor of the bulb, the
voltage across the bulb terminals is limited by the neon lamp's firing voltage
to approximately 90
Volts AC. In other words, the current flows in the neon circuit path,
effectively bypassing the
internal capacitor of the CFL bulb. To counter this effect, the bypass
capacitor 274 provides an
alternate resonant path consisting of the inductor 230 and the bypass
capacitor 274, which enables
the voltage to reach sufficient firing voltage for the CFL bulb at a slightly
higher frequency than
when the inductor resonates with the internal capacitance of the CFL bulb
alone. The voltage
increases across the bypass capacitor 274 and provides current through the
bulb filaments until the
break-over or firing voltage of the bulb is exceeded. At that point the bulb
fires and the operating
frequency shifts back to its nominal operating value of approximately 32 Khz.
In operation, once the circuit has started, the electronic ballast circuit
produces an oscillating
square wave voltage across each of the first and second CFL bulbs 260, 266,
and a corresponding
oscillating current in each of the bulbs 260, 266. The frequency of the
oscillation is determined by
the values of the inductance of the inductor 230 or 234 and the series
combination of the capacitor
242 or 244 and the internal capacitance of the CFL bulb, in parallel with the
bypass capacitor 274 or
280. In the illustrated embodiment, the frequency is approximately 32 Khz. If
a CFL bulb burns out,
"23'"
CA 02622170 2008-02-25
in effect removing that bulb's internal3 nF capacitor from the circuit, the
frequency would tend to
rise to approximately 52 Khz were it not for the resettable fuse, which limits
the drive current to a
value insufficient to sustain oscillation in the disabled bulb circuit. When
the defective bulb is
removed, the lamp may continue operation with the other bulb, with no harm to
the non-operating
bulb accommodation circuit.
The CFL bulb characteristics are accommodated as follows. The purpose of the
capacitors
242 and 244 is to block direct current flow in the respective CFL bulb 260,
266, enabling only
alternating current to flow through the bulb. The purpose of the capacitors
274 and 280 is to enable
the electronic driver circuit 154 to start when starter type CFL bulbs are
used in the task 1amp, as
described supra. However, if a bulb 260, 266 burns out, the respective bypass
capacitor 274, 280 in
the circuit may permit the current in the lamp to build to an excessive level
when it resonates with
the respective series inductor 230, 234, resulting in damage to the ballast
circuit 150. The purpose
of the resettable fuse 276, 282 is to limit the current in the bypass circuit
until the defective bulb 260,
266 is removed. The resettable fuse is a positive temperature coefficient
resistor having a resistance
element that increases in value as the current through it increases. The
resettable fuse in the
illustrated embodiment is a type MF-R010 available from Bourns Inc.,
Riverside, California. The
resistance of the resettable fuse 276, 282 also damps any tendency of the
bypass capacitor to enter a
resonant state in combination with the respective series inductor 230 or 234.
The purpose of the
switch 272, 278 is to open the respective accommodation circuit 156 when a
defective bulb is
removed, thus permitting the remaining CFL bulb to continue operation. When a
bulb is installed in
its respective receptacle, the switch contacts are closed, connecting the
switch 272, 278 in series with
the bypass capacitor 274, 280 and the resettable fuse 276, 282 across the
terminals of the respective
CFL bulb 260, 266.
In the foregoing description of the bulb accommodation circuit 156, values
were disclosed for
the inductors 230, 234 and the capacitors in the circuit that affect the
frequency of resonance under
several conditions for the illustrated embodiment. When constructing other
embodiments of this
circuit, several factors about the component values should be kept in mind, as
will be understood by
24'"
CA 02622170 2008-02-25
persons skilled in the art. The dominant capacitance in the circuit is the
internal capacitance of the
CFL bulbs, which is approximately 0.003 uF (or 3 nF), and which may vary over
a fairly wide range,
depending upon the particular bulb manufacturer and the normal production
variations that may be
expected. It will be appreciated that the value of the blocking capacitor 242,
244, at 0.022 uF, is
much larger than the internal bulb capacitance, so that it will have only a
small effect upon the
resonant frequency because it appears in series with the internal bulb
capacitance. It will also be
appreciated that the value of the bypass capacitor 274, 280, at 0.0015 uF, is
substantially smaller than
the internal bulb capacitance, so that its affect upon the resonant frequency
is again relatively small.
In the latter case, the bypass capacitor, being in parallel with the internal
bulb capacitance, results in
a combined (it is additive) capacitance of approximately 0.0045 uF. This
combined capacitance is
in series with the blocking capacitor. Thus, the total capacitance, including
the blocking capacitor in
series with the 0.0045 uF combination, is approximately 0.0037 uF (or 3.7 nF),
which is still
relatively close to the nominal - and variable - internal capacitance of the
CFL bulbs. It is this total
capacitance which resonates with the inductors in each respective bulb
accommodation circuit 156 at
a frequency of approximately 32 Khz.
Referring to Figure 6 there is illustrated a pictorial view, partially
exploded, of one
embodiment of the assembly 300 of first and second CFL bulbs 260, 266 and
their receptacles as
employed in the fluorescent task lamp according to the embodiment of figure 1.
Portions of'the first
and second receptacles 158, 160 are shown, including first and second
terminals 250, 252 of the first
receptacle 158, as well as a second terminal 256 of the second receptacle 160.
The first CFL bulb
260, and its first and second terminals 262, 264 is shown removed from its
respective receptacle 158
but aligned therewith by the broken lines. The second CFL bulb 266 is shown
fully plugged into its
respective receptacle 160, with a first terminal 270 of the second CFL bulb
266 fully inserted into the
termina1256 of the second receptacle 160. Further, each of the first and
second CFL bulbs 260, 266
include a base 302, 304 respectively. Positioned in the lower portion of each
receptacle 158, 160 is a
SPST switch which completes the bulb accommodation circuits 156 as previously
described. When
fully inserted into its respective receptacle, the base 302 of the first CFL
bulb 260 operates the
movable contact 306 of the corresponding SPST switch 272 to close the switch
272 and connect the
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CA 02622170 2008-02-25
bypass capacitor 274 and resettable fuse 272 into the bulb accommodation
circuit for the first bulb
260. Similarly, when fully inserted into its respective receptacle, the base
304 of the second CFL
bulb 266 operates the movable contact (not visible in Figure 6) of the
corresponding SPST switch
278 to close the switch 278 and connect the bypass capacitor 280 and
resettable fuse 282 into the
bulb accommodation circuit for the second bulb 266.
The switches 272, 278 shown in Figure 6 are small micro switches configured to
be placed
just below the respective receptacles 158, 160 so that the depression of the
movable contact, e.g.,
contact 306, may cause the switch contacts inside the switch to close whenever
a bulb is fully
inserted into the respective receptacle. As persons skilled in the art will
realize, however, there are
many kinds of switch that may implemented in this example to fulfill the
function of the switch 272,
278. These may include, but are not limited to, switches (not shown) operated
by optical (photo
diode) devices, Hall effect or reed switch mechanisms, or simply a pair of
beryllium-copper contact
strips secured in the receptacles themselves and configured to be closed by
the insertion of the bulb
into the receptacle. Moreover, the switches may be utilized to control other
functions in the
electronic ballast circuit 150 of the present disclosure.
Referring to Figure 7 there is illustrated an exploded view of major
components of the
fluorescent task lamp 10 according to the embodiment of Figure 1, as viewed
from a perspective
below and rearward of the task lamp 10. Included are the housing 12, the clear
lens body 14, the
elongated spine 16, the flexible cap 18, the closed end 20 of the lens body, a
first CFL bulb 22, the
resilient bulkhead 26, the reflector 30, the integral base 34, the line cord
38, the pivoting strain relief
40, the ON/OFF switch 164, and the rod 42 that supports the hooks 46 having
the nylon tips 48, all
of which were previously described in the description of Figures 1 and 5
supra. In order of
assembly, the reflector 30 is attached to the forward face of the reflector
panel 58 using an adhesive,
the first and second (not shown in Figure 7) CFL bulbs 22, 24 are installed in
their respective
receptacles (not shown in Figure 7), the resilient bulkhead 26 is inserted
into the interior of the lens
body 14 to a position approximately 3/8 inch from the closed end 20 of the
lens body 14, and the first
and second rails 55, 57 molded into the reflector panel 58 of the lens body 14
are aligned with the
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CA 02622170 2008-02-25
corresponding grooves 54(not visible in Figure 7), 56 formed into the edges of
the elongated spine
16 (as previously described in the description of Figure 2 supra), and the
lens body 14 is pushed
along the rails 55, 57 and grooves 54, 56 until it is seated within the open
end 15 of the housing 12.
Other features of the task lamp 10 visible in Figure 7 but concealed in the
previous F'igures 1
and 2 include the flat bottom 314 of the integral base 34 and the pivoting end
316 of the pivoting
strain relief 40 that pivots within an opening 317 of the housing 12 about a
strain relief pivot pin 318
passing through the sides 319 of the opening 317. As indicated by the
positions 320 and 322, shown
in phantom, the pivoting strain relief 40 swings through an angle of
approximately 90 degrees
between the upper position 320 that is approximately perpendicular to the rear
of the housing 12 and
the lower position 322 that is approximately parallel to a longitudinal axis
of the housing 1.2. This
range of motion enables the line cord to be positioned out of the way and/or
at an angle that permits
the task lamp 10 to be stood on its base or hung by its hooks in a natural
manner.
At the opposite end of the task lamp 10 shown in Figure 7, the flexible cap 18
includes an
interior surface 330 that is fonmed with several low profile ribs 331 that
function to retain the cap 18
on the closed end 20 of the lens body 14. The flexible cap 18 further includes
a bore 332 for
receiving the post 42 therein. The bore 332 provides a slightly interfering
fit for the post 42, such
that the post 42 may be moved rotationally and longitudinally within the bore
332 yet retained by the
friction of the interfering fir when the post is adjusted by the user to
position the hooks 46 in a
particular orientation. For example, the hooks 46 may be moved longitudinally
between the
extended 340 and retracted 342 positions, or rotationally through an angle of
360 degrees (not
shown). Also visible on the lower end of the post 42 is a rounded knob 43 that
functions to retain the
post 42 captured within the cap 18. When in the retracted position the post 42
is stored within a
passage 336 molded into a bulge 44 in the rearward side of the elongated spine
16, as will be
described infra.
Still other features of the task lamp 10 visible in Figure 7 but concealed in
the previous
Figures 1 and 2 include an upper or distal end 17 of the elongated spine 16, a
mounting tab 350
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CA 02622170 2008-02-25
having one or more mounting holes 346 (two are shown) and formed into an upper
end of the
backside of the lens body 14, and a bulge 44 formed into the rearward side of
the elongated spine 16.
The bulge 44 increases the cross section of the elongated spine 16 to provide
greater strength and
provides space within it to accommodate the movement of the post 42 that
supports the hooks 46 in
an adjusted position. Further, the distal end 17 of the elongated spine 16
includes one or more
mounting holes 342 therethrough for receiving the one or more mounting screws
344 for securing the
lens body 14 to the distal end of the elongated spine 16 during assembly. The
distal end 17 of the
elongated spine 16 may also include several low profile ribs 338 to engage
with the low profile ribs
331 within the cap 18. Together, the ribs 338 and 331 help to retain the cap
18 in place on the lens
body 14.
Referring to Figure 8 there is illustrated a pictorial view of separated first
360 ancl second
362 halves of the housing of the fluorescent task lamp 10 according to the
embodiment of Figure 1,
wherein the electronic ballast circuit board 364 is installed in the handle
portion of the second half
362 of the housing 12. A corresponding space 366 is provided in the first half
360 of the handle
portion of the housing 12 to accommodate electronic components of the
electronic ballast cir=cuit 150
(See Figure 5). Some of these electronic components include the pulse
transformer 222 and the first
and second inductors 230, 234. It will be appreciated that, in the illustrated
embodiment, the
elongated spine 16 is an integral extension of the housing 12 because each
half of the housing
assembly is a single molded part. This construction and the material selected
are chosen to provide
the necessary strength and a prescribed amount of flexibility such that the
combination of the
housing 12 and elongated spine 16 assembly can support and protect the more
vulnerable
components of the task lamp 10. The result is a housing assembly that
distributes impact forces from
mechanical shock to minimize the effects on the relatively fragile CFL bulbs
and other vulnerable
components. In other embodiments, the elongated spine 16 and the housing 12
may be configured as
separate components provided they are designed to take into account the
strength and shock
absorbing requirements noted herein above.
v28-
CA 02622170 2008-02-25
It was previously mentioned in the detailed description of Figure 2 that the
elongated spine 16
includes a hollow space 50 within it. This space is the same as the space 368
designated within each
of the first 360 and second 362 halves of the elongated spine 16 shown in
Figure 8. The space 368
may be used to enclose wiring or circuitry for additional features of the task
lamp 10. Such
additional features may include but not be limited to point source light
emitting devices, lighting
controls, metering or status indicators, connectors for auxiliary devices, and
the like.
All of the other features identified in Figure 8 have been previously
described and bear the
same reference numbers referred to in those descriptions. These features
include the housing 12, the
elongated spine 16 and its distal end 17, the finger grip 32, the integral
base 34, AC outlet. 36, line
cord 38, pivoting strain relief 40, and the bulge 44 in the elongated spine
16. It will be further noted
that the wiring 380 (including three conductors for line, neutral and ground
wires) connecting the
conductors enclosed within the strain relief 40 to the AC outlet and the
circuit board 364 include a
prescribed amount of excess length to enable the pivoting of the strain relief
40 with minimal flexing
of the wiring 380. Other features previously described also include the first
receptacle 158, the
ON/OFF switch 164, the flat bottom 314 of the integral base 34, the pivoting
end 316 of the pivoting
strain relief 40 and the strain relief pivot pin 318. Also shown in Figure 8
are open mounting holes
370 in the second half 362 of the housing 12 and elongated spine 16 (See six
places) and bosses 372
(See six places) in the first half 360 of the housing 12 and the elongated
spine 16 for receiving
mounting screws (not shown) for securing the first 360 and second 362 halves
of the housing 12 and
elongated spine 16 together. The inclination angle between the longitudinal
axes of the housing 12
and the elongated spine 16 is approximately 9 degrees for the embodiment
shown, as previously
described.
The principles of the pivoting strain relief described herein above for a
handheld fluorescent
task lamp may be applied to other types of electrical appliances such as
electrically powei-ed hand
tools, cleaning and lighting implements, and the like. Referring to Figure 9
there is illustrated a
pictorial view of separated first and second shells of a housing and strain
relief for an electrical
appliance according to an alternate embodiment of the invention. While the
illustrative embodiment
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CA 02622170 2008-02-25
to be described resembles that fluorescent task lamp illustrated in Figures 1
through 8, the swiveling
strain relief feature of the housing assembly may be advantageously
incorporated in other types of
electrical appliances. In the description which follows, structures of Figure
9 in common with
identical structures shown in previous figures, for example Figures 7 and 8,
bear the same reference
numbers.
Continuing with Figure 9, portions of one end (as shown, a bottom end 314 in
the figure) of
the first and second shells 360, 362 of the housing 12 are shown separated but
approximately aligned
for assembly along the proximate edges of each first and second shell 360, 362
as they are brought
together. Positioned between the first and second shells 360, 362 is a strain
relief 40 disposed on an
end portion of a power cord 38. The power cord 38 may include a plurality of
conductors 380 to be
connected to various parts of an electrical circuit within the housing 12. The
strain relief includes a
hub portion 316 having first and second pivot pins 318 extending from each
side of the hub portion
316 and oriented along a common axis. Upon assembling the first and second
shells 360, 362 of the
housing 12 together, the first and second pivot pins 318 are placed within the
first and second pivot
bushings 382, thus capturing the hub portion 316 of the strain relief 40
between the first and second
side walls 384 of an aperture or cavity 386 formed in the housing 12. A dashed
line extending from
each pivot pin 318 denotes an approximate path of the axial centerline of the
bushings 382 as the
first and second shells 360, 362 are brought into position against each other
and the pivot pins 318
are inserted into the pivot bushings 382. The first and second shells 360, 362
may be secured
together by any of several well known means, including the method described
for the embodiment of
Figure 8 herein above, and will not be further described herein.
As will be apparent from a study of Figure 9 and also Figure 7, the first and
second side walls
384 of the aperture or cavity 386 formed in the assembled housing first and
second shells :360, 362
are substantially parallel mirror images of each other. Thus, when the hub
portion 316 of the strain
relief 40 is in position within the aperture or cavity 386, the sides of the
hub 316, also being
substantially parallel may be in contact with the side walls 384 of the
aperture or cavity 386. In a
preferred embodiment, the distance between the first and second side walls 384
when the first and
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CA 02622170 2008-02-25
second shells of the housing 360, 362 are assembled is predetermined to be
slightly less than the
thickness 396 of the hub 316 to provide an interference fit between the hub
316 and the side walls
384. The resulting friction enables the pivoting strain relief 40 to remain in
an orientation given to it
by the user. This effect of the spacing may be enhanced by fabricating the
strain relief 40 of a
material that is somewhat resilient and/or includes a non-skid surface
characteristic. A preferred
material will be described further herein below.
In use, when the housing 12 is stood on its first end or base end 314, the
power corcl may be
oriented substantially away from or perpendicular to the longitudinal axis of
the housing as shown in
the dashed lines 320 of Figure 7 and held in that orientation by the friction
resulting from the
interference fit between the hub 316 of the strain relief 40 and the side
walls 384 of the aperture 386
in the housing 12. Similarly, when the housing 12 is supported from its
second, opposite end, the
power cord may be oriented or "dangled" substantially along or in parallel
with the longitudinal axis
of the housing as shown in the dashed lines 322 of Figure 7 and held in that
orientation by the
friction resulting from the interference fit between the hub 316 of the strain
relief 40 and the side
walls 384 of the aperture 386 in the housing 12.
The orientation of the power cord strain relief 40 may be positioned anywhere
within a range
of at least approximately 90 as indicated above, between an orientation
approximately parallel with
the longitudinal axis of the housing 12 and an orientation approximately
perpendicular to or normal
to the longitudinal axis of the housing. The orientation positions may be
determined and liinited by
lower and upper stops, 392, 394 that are formed in the first and second shells
360, 362 of the housing
12 and will be further described in conjunction with Figure 10.
The elastomeric material preferred for fabricating the strain relief 40 has
been experimentally
determined to be polyvinyl chloride ("PVC") impregnated with approximately 5%
nylon and 3%
plasticizer. Further, the material should preferably have a durometer of
approximately 70 to 80 on the
Shore "A" Scale. The nylon provides the necessary strength and the plasticizer
mitigates the inherent
hardness of the nylon ingredient. The strain relief 40 is preferably molded as
a single coinponent
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CA 02622170 2008-02-25
having an integral hub portion 316 and be within the aforementioned durometer
range to provide the
flexibility, resilience, strength and non-skid surface characteristics
necessary to enable pivoting
adjustment of the power cord orientation while securing and maintaining the
line cord in a correct
orientation and entry into the housing of the appliance despite being subject
to frequent and
sometimes forceful adjustment. One important property of the hub portion 316
of the strain relief 40
for certain product applications is that the power cord 38 secured by it be
able to withstand
substantial loading where the appliance must comply with the specifications of
recognized test
laboratories for an intrinsically safe appliance. Thus, if the power cord 38
must support, e.g., a test
pull in excess of 35 pounds, the pivot pins 318 molded into the structure of
the hub 316 must be
strong, relatively rigid, and of sufficient dimension to withstand such
tension.
Another important property of the strain relief 40 is its alternating ribbed
configuration
surrounding the power cord, which by distributing the bending stresses along
the power cord 38,
diminishes the amount of stress at any specific point to relieve the strain on
the cord itself. This
stress is relieved partly by the array of discs disposed in close proximity
along the cord that passes
through the centers of the discs. Upon bending, the adjacent edges of the
discs contact each other
along the inside of the bend in the cord to limit the amount of bending at
that location. In the
aggregate, the plurality of discs distribute the bending stresses.
In the foregoing description, the illustrative example assumed the cord being
protected by the
strain relief is a power cord for the electrical appliance. However, as will
be apparent to persons
skilled in the art, any kind of flexible cord or cable or other slender tubing
or cord-like coinponent
may be advantageously provided entry to the appliance using the strain relief
disclosed herein.
Referring to Figure 10 there is illustrated a side view of a strain relief 40
installed in one
shell of the housing 12 of the embodiment of Figure 9. In the description
which follows, structures
of Figure 10 in common with identical structures shown in previous figures
bear the same reference
numbers. The strain relief 40 is shown in position relative to the first shell
360 of the housing 12 and
the lower stop 392 and upper stop 394 thereof. The lower and upper stops 392,
3941imit the rotation
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CA 02622170 2008-02-25
of the hub portion 316 if the strain relief 40 as it is swung to a desired
position or orientation. The
lower stop 392 limits the rotation to an orientation approximately parallel to
the longitudinal axis of
the housing 12. Similarly, the upper stop 394 permits rotation of the strain
relief up to approximately
120 relative to the downward-extending position determined by the lower stop
392. The limit
orientations are represented by the dashed lines 320 and 322 and the arc line
398, corresponding to
the maximum longitudinal and lateral extensions of the strain relief 40 in the
illustrated embodiment.
The 120 range includes the orientation normal to the longitudinal axis of the
housing 12, but
permits some rotation beyond the "normal" position for some applications. The
position of the stops
may be varied to provide different orientations.
While the invention has been shown in only one of its forms, it is not thus
limited but is
susceptible to various changes and modifications without departing from the
spirit thereof. For
example, while the self-starting electronic driver circuit in the electronic
ballast is illustrated for use
with two 9 Watt CFL bulbs, the circuit is readily scalable for other bulb
ratings or power
requirements by an appropriate change in the component values, such as the
inductance, capacitance
and resistance values of the passive components, current, voltage, and
dissipation ratings for the
semiconductors, etc. Substitutions in the materials are also possible, keeping
in mind the functions
performed, as new materials become available or new applications demand that
different materials
than those suggested for the illustrative embodiment. The present invention
may further be
configured for operation from other values of AC operating voltages than the
120 Volts AC 50/60
Hz such as 208, 220, or 240 Volts AC, 50/60 Hz. 400 Hz power may also be used
with appropriate
modification to the components selected.
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