Note: Descriptions are shown in the official language in which they were submitted.
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PROTECTIVE COVER FOR AN INFRARED
THERMOMETER
Field of the Invention
The present invention relates generally to protective covers for infrared
sensor systems. In particular, the present invention relates to an enhanced
protective cover design that permits passage of infrared radiation with a minimal
of distortion while insuring sanitary protection of an infrared clinical
thermometer.
Backqround of the Invention
Accurate temperature measurement has long been an objective of
researchers in a variety of fields. Temperature sensing of patients is of
particularly acute concern in the health care field due to the high correlation
between patient health and body temperature. Indeed, a significant aggregate
expenditure in support of medical care is dedicated to the accurate assessment
of body temperature - in hospitals, clinics, nursing homes, doctor's offices and,
of growing importance, at home. Invariably, one of the first things sought during
a visit to a doctor or hospital is the patient body temperature. As such, patient
temperature ~ssessment is a large and important expenditure in providing
sùitable health care.
Past patient temperature measurement systems have migrated from slow
mercury thermometers (oral and rectal) to 01e~nic contact sensors (predictive
thermometers using resistive contact elements) to more recent non-contact
systems based on infrared ("IR") sensing. A particularly successful clinicaJ
thermometer cor,esp~nds to U.S. Paterit No. Re: 34,789 to Fraden (the "Fraden
IR Thermometer") the contents of which are incorporated by reference as if
restated in full. The Fraden design utilizes a highly sensitive infrared detector
engineered with a specific optic system to permit accurate assessment of
~ radiation from the tympanic membrane of a patient's ear. The sensed radiation
is converted to a temperature reading having an impressive correlation to actualpatient temperature. Importantly, the above design permits accurate
temperature measurement in 1-2 seconds with minimal patient discomfort.
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Clinical practice mandates a sanitary environment for the patients and
instruments. Disposable sanitary protective covers have become an ubiquitous
commodity in patient carei minimizing the spread of infectious agents and
cross-contamination of patients under care in a common area. The needs ~or
5 sanitary practice also exist in the use of IR thermometers. Accurate
temperature measurement with an IR thermometer requires the controlled
placement of the sensor probe into the patient's ear canal for proper alignment
between the IR sensor and the tympanic membrane of the ear. The ear canal
is not a likely source of germs or other contar"inants - however, medical care
10 mandates the reduction of risk of cross contamination whenever possible.
Additionally, the optics of an infrared thermometer must remain free and clear of
ear wax. In view of the foregoing concerns, use of the minimally intrusive
infrared thermometers of the Fraden type is advantageously implemented with a
sanitary barrier precluding contac~ between the sensor and the patient's ear.
Sanitary barriers for clinical thermometers are not new. Indeed, many
older clinical thermometers based on contacting mucous membranes for
sensing temperature required the use of a disposahle cover as a sanitary
barrier, which was discarded afler each use. Early sanitary cover designs were
quite simple in concept. The basic structure applied a rigid wall for handling
purposes combined with a thin film contiguous with the contact sensor element.
The film was thin and often stretched to minimize the thermal barrier to
conductive heat transfer. Exemplary early cover structures are depicted in U.S.
Patent No. 3,822,593 to Oudawaal and Patent No. 3,987,899 to Vyprachticky.
These early covers were routinely made from inexpensive plastics such as
polyethylene and polypr~,pylene and either injected molded as one unitary
structure or formed in two parts - bonding a thin film onto the more rigid body
portion. Either way, the resulting cover would be attached to the sensor and
then the combined structure placed, e.g., in the patient's mouth to obtain the
temperature reading. After the reading, the cover is detached and discarded.
Early infrared thermometers also employed disposable covers. These
early disposable covers for infrared thermometers originally were closely
modeled on the above-described covers for contact thermometers. For
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example, U.S. Patent Nos. 5,293,862 and 5,179,936 to O'Hara, et al. disclose
a two-piece cover design wherein a thin transparent film is bonded to a rigid
tubular body forming a disposable cover for an infrared thermometer. The
manufacturing process of this cover design c~uses the formation of wrinkles in
5 the thin transparent film. Film wrinkles of this nature may interfere with infrared
transmission between the tympanic membrane of the ear and the IR sensor of
the thermometer. Accordingly, the use of this probe cover design required the
removal of these wrinkles by stretching the film over the infrared sensor.
However, stretching the film to remove wrinkles may create other sources
10 of potential measurement inaccuracies. Firstly, a film that is stretched may
stretch in a non-uniform manner creating a "lensing" effect that may distort
transmitted infrared radiation. Secondly, the stretched film may result in a
realignment of the polymer molecular structure causing variations in both the
reflective and absorptive properties of the film. Accordingly, such prior art
15 infrared probe covers that require slretcl,ing to remove wrinkles or other
undesirable surface characteristics in the film window of the disposable cover
may possess somewhat unpr~ict~ble transmission properties when fitted onto
a probe of an infrared thermometer.
Similarly, U.S. Patent No. 4,9~1,559 issued to Meist and Suszinski
20 discloses an infrared probe cover susceptible to the effects of s~ tching of the
film. The Meist and Suszinski patent teaches a laminated probe cover where
the polymer film significantly stretches when being fitted over an infrared
thermometer probe. The effects caused by this stretching of the film invariably
affects the transmissivity of the film in unpredictable ways that may result in
25 errors in temperature measurement. -
Other problems have arisen with past designs of probe covers forinfrared sensors. For example, prior art infrared probe covers were often
configured so that the film would contact the patient skin. The patient skin - if
at a different temperature than that of the probe cover - will cause a
30 temperature gradient to form in the film as heat conduction triggers an energy
flow from the warmer ear to the cooler film. The resulting elevated temperature
of the film amplifies an error source known as secondary radiation. Secondary
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radiation refers to the infrared radiation that the cover emits relative to the
infrared radiation emitted by the primary source, vlz., the tympanic membrane ofthe ear. It has been found that it is important to minimize the fluctuations of
secondary radiation from all sources including that of the cover film window.
Secondary radiation triggered by unpredictable heat flows from the ear canal to
the film window may induce measurement inaccuracies in the clinical
thermometer.
An additional source of measurement error resides in the departure from
good optical alignment that characterized earlier cover designs. For example,
the prior art covers with non-uniform film windows (caused by either the
manufacturing process or subsequent stretching) are haphazardly placed on the
sensor with no ability to control the alignment of the film window relative to the
sensor - target optical axis. Consequently, if the probe cover is not properly
aligned or centered, the transmission of infrared radiation may be affected due
to variations in the film.
Experience in clinical thermometer use has shown that it may be
desirable to increase the angle of view of an infrared sensor. It is believed that
the enhanced angle of view compensates for directional errors that may arise if
the clinical thermometer is not properly inserted in the ear canal for a
measurement, i.e., the sensor is not properly aligned with the tympanic
membrane as incor,ectly aimed. Probe cover designs that excessively limit the
field of view of the IR sensor may become an impediment to proper temperature
~ssessment.
As can be seen from the above discussion, the design of infrared
2~ transmissive disposable covers is a complex and difficult task. The recognition
of the need for a fully functional sensor cover design and the inherent problemsof the prior art have led to the present invention.
SummarY of the Invention
Accordingly, it is an objed of the present invention to provide a probe
cover design that eliminates the stretching of the film window portion of the
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probe cover so that stretched induced distortions are removed as a source of
. measurement errors in clinical temperature measurement.
It is another object of this invention to minimize the thermal effects which
result from contacting the probe cover with the skin surface of a patient.
Another object of this invention is to provide a self-aligning probe cover
- which would ensure consistent placement and optical alignment of the probe
cover onto the thermometer probe.
Still another object of this invention is to provide a probe cover which
enhances the field of view of the infrared thermometer, thereby minimizing
errors in the placement of the thermometer probe within the ear canal.
The above and other objects of the present invention are realized in a
protective cover design that includes a window portion having a pre-engineered
set of IR transmission characteristics that eliminate the need to stretch the film
window or otherwise manipulate the film window after manufacture. As with
prior art protective covers, the inventive cover includes a side wall section that
is designed to engage the thermometer probe section and position the
transparent film window in front of the sensor. The preferred shape is a short
truncated cone or tubular structure open at a first end and closed with the filmwindow positioned at a second and opposing end of the tubular body. The
open end is dimensioned and adapted so that it interfaces with the probe tip of
the thermometer to releasably hold the cover in an automatically centered
position in relation to the probe sensor.
The IR transmissive film is preferably a circular window with a
circumferen~ial strain relief collar extending around the window perimeter. Thiscollar defines and controls the shape of the film window. When placed on the
thermometer, this collar engages a cor,esponding contact rim on the probe, thus
positioning the film window in the proper optical axis for the IR sensor.
Furthermore, the collar provides a strain relief capability corresponding to itsdeformation under load that insures that the window section is held in an
"unstretched" condition. The collar location and configuration further acts to
maintain the proper optical axis when the thermometer is in use.
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In accordance with the varying aspects of the present invention, the
disposable cover includes a side wall that is kept relatively thin and thus
preferentially deformed relative to the film window when forces are applied to
the cover. These forces act on the side wall and impinge on the collar of the
film window. Accordingly, the collar structure can follow one of several distinct
design approaches, each having the common goal of either eliminating the
transfer of forces applied to the cover side wall (isolation), or creating counter
forces in reaction to the forces applied to the side wall (strain reliefl where these
counter forces are of a nature and direction that precludes film stretch.
Additionally, the functional collar design acts to deflect the film window away
from contact with the ear canal, while enhancing the overall field of view for the
sensor.
Another design feature is directed to the cover retenlion means placed,on
the wide, open end of the cover and configured to engage a pair of retention
"ears" on the base of the probe. Controlled positioning of the cover vis-a-vis the
probe is used to enhance window stability and minimize probe tip contact with
the window. This is acco""~lished by creating a tight engagement rim having
an expanded radius. Separately, a small air slot is provided as a pressure relief
point.
The foregoing features of the present invention are more fully and readily
understood from the following detailed description of specific illustrative
embodiments thereof, presented l,ereinL,elow in conjunction with the
accompanying drawings of which:
Brief DescriPtion of the Fiaures
Figure 1 depicts a probe cover being placed on the probe of an infrared
thermometer;
Figure 2 is a conventional probe cover with a stretched film window
portion;
Figure 3 depicts an improved probe cover with recessed front end;
Figure 4 is an enlarged portion of the front end of the improved probe
cover;
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Figure 5 depicts corrugated optical portion of a probe cover;
Figure 6 is an exploded view of the corrugated film at the optical portion
of a probe cover;
Figure 7 depicts a probe cover with a collar frame for the film window
Figure 8 depicts a variation of the cover shown in Fig. 7;
~ Figure 9 depicts a cut-out view of a film window with a dimpled surface;
Figure 10 depicts a probe cover collar structure with variable thickness
strain relief;
Figures 11 and 11A depict a probe cover collar structures with collapsing
strain relief;
Figure 12 is another embodiment depicting collapsing strain relief;
Figure 13 provides a variation of the improved probe cover of Fig. 12;
Figures 14A and 14B depict a further cross-sectional diagram of an
inventive cover in accordance with the present invention and an enlarged view
of its collar structure also in cross-section; and
Figures 15A, 15B, and 15C depict a novel probe cover structure with
retention rim, an enlarged view of the retention rim, and view of selected
reference dimensions of the probe cover.
For convenience of reference, like components, elements and features in
the various figures are designated by the same reference numerals or
characters.
Detailed DescriDtion of sDecific Embodiments of the Invention
First briefly in overview, the present invention is directed to novel probe
cover configurations engineered for enhanced use with clinical thermometers
applying infrared temperature detection. The inventive probe cover
configuration provides an infrared transparent window that, in its initial, stress-
free condition, is optimized for infrared radiation transmission. The window is
formed of a highly transmissive polymer material and configured to minimize the
potential error sources found in prior art designs.
The inventive probe design is further engineered to prevent subsequent
forces from distorting the IR window during use. There are at least two sources
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of window distortion forces applied to the probe cover. The first distortion force
is applied during the probe cover installation onto the thermometer probe tip.
As discussed above, the probe cover should be affixed to the probe in a
repeatably accurate operation. This attachment process invariably imparts a
5 force to the cover structure. It is, therefore, a feature of the present invention to
isolate the IR window portion of the cover from the attachment forces
encountered during cover installation.
The second source of distortion forces to the cover arises during a
temperature reading. To take a reading, the cover/probe is inserted into the ear10 canal to create the re~uisite optical axis between the tympanic membrane of the
ear and the IR sensor imbedded in the clinical thermometer. The sliding action
of the cover wall against an inner ear canal creates smatl frictional forces on the
cover. Accordingly, it is a second feature of the present invention to isolate the
IR transmission window from these frictional forces that may arise during the
15 actual temperature acquisition process.
The force isolation described above is accomplished by use of a collar
structure juxtaposed between the side wall of the cover and the film window. In
this context, the term "collar' is broadly used to include one or more structural
elements that are applied individually or in combination to either isolate the
20 window from wall forces, enhance sensor view, minimize sensor - ear canal
contact or create counter forces to negate the translation of wall forces to thefilm window.
In addition to the foregoing considerations, enhanced cover design is
enabled by selective dimensioning of the retention rim of the probe cover
25 relative to the corresponding probe retaining ears. In particular, to preventvertical movement of the cover relative to the probe, the cover rim or "locking
groove" is sized to fit snugly on the retaining ears of the probe by establishing
two separate planar points of contact, thus eliminating any "play" that might
otherwise permit such freedom of movement. This is accomplished by creating
30 a tight tolerance between the cover locking groove - and its circumferential
dimension, and the circumference defined by the outer position of the retaining
ears. This alone, however, may cause the cover placement procedure to
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require an excessive amount of force. The additional force requirement caused
by the tighter tolerance accrues from the need to expand the locking groove
diameter as the cover is pushed over the retaining ears - an expansion of the
elastic hoop. In some instances, especially those that involve a separate cover
5 ejector mechanism, the additional force for attachment of the cover is excessive
for its intended purpose. Accordingly, the attachment force is appropriately
controlled by enlarging the partial radius of the locking groove. This lowers the
angle of the groove lip and allows less force for installation even with the tighter
tolerances.
With the foregoing brief overview in mind, attention is first directed to
Figs. 1 and 2 and the general arrangement of the cover- IR thermometer
depicted therein. Fig. 1 illustrates the positioning of an infrared probe cover 8
having optical film window 10 as placed over the elongated probe 2 of infrared
thermometer 1 (as illustrated by phantom lines). In this instance, probe 2 is
15 appropriately sized for insertion within the ear canal of a human or animal, but
also can be used for taking temperature measurements from any other body
cavity or surface. Probe 2 houses an infrared sensor 3 and optical wave guide
4 and is able to measure the transmission of thermal radiation from a patient's
ear 5, which emanates from the tympanic membrane 7 of ear canal 6. It should
20 be noted that the temperature of the tympanic membrane 7 represents an
accurate reading of the interior temperature of a patient's body.
The probe cover 8 is positioned over probe 2 of the thermometer and
aligned along optical axis 9 of the probe such that there can be no physical
contact between probe 2 and any part of the patient's body, particularly ear
25 canal 6. This insures sanitary operation. As shown in Fig. 1, the probe coverconsists of three primary portions: a back end portion 30 for engaging the probecover with infrared thermometer 1 along probe 2, an intermediate sidewall 31
which extends the length of probe 2, and an optical front end portion, includingfilm window 10 with the requisite optical and thermal properties necessary for
30 the accurate transmission of infrared radiation and, accordingly, to provide an
accurate measurement of temperature.
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Preferably, the material for the probe cover is a polymer such as
polyethylene, polypropylene, or copolymers thereof having a transparency in
the spectral range between 3~m and 15,um. Often the polymer used can be
optically enhanced by the addition of clarifying agents in the polymeric matrix. It
is not necessary that the sidewall material be the same as the film window. If
however, the cover is a unitary structure, the material will be the same for both
the side wall and film window. See, e.g., U.S. Patent No. 5,088,834 to Howe,
et al. disclosing a unitary cover configuration for an IR thermometer (the
contents of which are incorporated by reference). The preferred manufacturing
process is by vacuum forming a plurality of separate covers from a large sheet
of thin polypropylene co-polymer. Alternative techniques for manufacturing the
cover include other thermoforming techniques and injection molding. If made of
separately cast components, the cover components are connected by means of
bonding, ull,~sonic welding, clamping or adhesive joining. If separate, the cover
window material should be highly transmissive to IR radiation when joined or
attachea to the sidewall.
Fig. 2 provides a cross-section view of a prior art probe cover 21
positioned over probe 2. As shown in Fig. 2, probe 2 has optical axis 9, wave
guide 4 with wave guide window 15, and rim 11. When probe cover 21
interfaces with rim 11 of probe 2, stress is applied to the optical film window 10,
resulting in a stretching of the film of the optical front end. Also, as shown in
the figure, back end portion 30 of cover 21 engages with probe 2 of the infraredthermometer (not shown) and sidewall 31 extends over the length of probe 2.
As probe cover 21 is fitted over probe 2, the resulting changes in thickness of
the film of the film window 10 due to stretching causes inevitable variations inthe optical transmissivity of the front end. Additionally, when stretched, film
window 10 may come into contact with the patient, absorbing heat and causing
a temperature rise that may alter the temperature reading of the infrared
thermometer. Accordingly, in prior art probe covers of this type, the stretched
film window may cause the infrared thermometer to render inaccurate readings.
Fig. 3 illustrates a cross-section view of a probe cover 8, depicting a first
embodiment of the present invention, as positioned over probe 2. Film window
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11
10 of the cover forms a recess connected to sidewall 31 via collar 34
comprising a sill 14 with first fold 12 and second fold 16. The depth of the
recess is, preferably, in the range from 0.2mm to 2.0mm. Sill 14 provides
perimeter stiffness to the structure of the probe cover, particularly to the front
5 end portion, in addition to providing a strain relief function for the film window.
Sill 14, which may be circular in shape, consists of folded polymer material
disposed around the periphery of film window 10. First fold 12 is provided
adjacent the recess of the film window 10 and second fold 16 is provided
adjacent the sidewall 31.
As shown in Fig. 3, when probe cover 8 is positioned over probe 2 of an
infrared thermometer, the cover interfaces with rim 11 of the probe at second
fold 16 of sill 14. The probe cover 8 is dimensioned for an interference fit with
probe 2 and since rim 11 of probe 2 closely interfaces with cover 8 near second
fold 16, the film window 10 is automatically centered along optical axis 9 of
15 probe 2, thus assuring consistent placement of the cover onto the probe. It
should be noted that film window 10 is kept separated from wave guide 4 and
from wave guide window 15 by air gap 13. Film window 10 is removed from
contact with a patient's skin by means of sill 14 and first fold 12, while at the
same time, ensuring that a smooth, continuous contact surface area is provided
20 at the front end of the cover, which is essential for patient comfort. In this
probe cover arrangement, recessed film window 10 is not subjected to stress
when the cover is posi~ioned over probe 2 and is, thus, able to maintain its
original shape, as well as its optical properties. In addition, because this probe
cover structure removes the film window from contact with a patient's skin, more25 accurate temperature readings are possible due to the elimination of any
secondary radiation.
Fig. 4 illustrates an exploded cross-section view of a portion of probe
cover 8 whereby the thickness of the polymer material of the cover is shown in
more detail. As shown in the figure, increased thickness of the sill 14, second
30 fold 16 and/or other portions of the cover may be provided. Increased thickness
near sill 14 andtor lower fold 16 may be beneficial for enhancing the strain relief
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12
function, as well as ensuring a better engagement by the cover onto the
thermometer probe.
Fig. 5 illustrates a cross-section view of an alternative embodiment of the
probe cover for the present invention. This embodiment is beneficial for further5 enhancing strain relief in the front end of the cover. As shown, cover 8 has acorrugated film window 23 with concentrically arranged ridges forming a series
of folds 17 and a central flat 18, which represents a non-corrugated area.
Preferably, flat 18 should have a diameter comparable with that of wave guide
4. Alternatively, flat 18 may be eliminated so that the corrugated surface
10 extends to optical axis 9. Regardless of whether nat 18 is provided, however, it
is desirable to maintain the thickness of folds 17 and flat 18 between 20 ~m and100 ~Jm, otherwise attenuation of the infrared radiation signal and/or absorption
of extraneous thermal energy by the cover membrane may result, thereby
causing an erroneous temperature reading by the infrared thermometer.
An enlarged cross-section view of a portion of the cover as referenced in
Fig. 5 is illustrated in Fig. 6. The multiple folds 17 of corrugated film window 23
of probe cover 8 provides the additional benefit of increasing the angle of viewof the infrared thermometer. As shown, folds 17 may be provided with a varied
thickness so that the folds consist of thick portions 20 and thin portions 19. The
variations in thickness of the folds provide a lensing effect due to the refractive
properties of the polymer material used for the cover. Accordingly, infrared
radiation 22 (as shown by the dotted line) which may be directed from a wide
angle direction onto the corrugated film window 23 is caused to refract at a
more acute angle toward the wave guide due to the varied thickness of folds 17.
In a corrugated film window 23 without folds, wide angle infrared radiation 22 is
reflected from the flat surface of the cover and, consequently, does not enter
the probe.
Figs. 7 and 8 provide enlarged cross-section views of a portion of the film
window 10 of a probe cover in accordance with the present invention. As
.30 shown in Fig. 7 and Fig. 8, collar 34 is provided around the film window 10.
Fig 7 illustrates such a probe cover collar with raised sill 14, while Fig. 8
illustrates such a probe cover collar with a flat sill. As shown in both figures,
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13
collar 34 provides a semi-rigid frame for the film window 10, thus ensuring thatthe film window remains free from forces otherwise applied to sidewall 31 and
after placement of the cover onto the probe. As shown in Fig. 7, care needs to
be taken when the probe is positioned inside the cover to ensure that
engagement force 35 is applied in a direction as shown in the figure, and not inan incorrect direction 36, which could result, if substantial, in potential stress on
the diameter of collar 34 stretching the film window 10.
Fig. 9 illustrates a cross-section of another embodiment of a probe cover
in accordance with the present invention. This particular embodiment offers an
alternative way to relieve the stress susceptible in the film window of the probe
cover, while minimizing contact of the cover with a patient's skin. As shown, the
cover is positioned over probe 2, with the film window 10 positioned over wave
guide window 15 and containing uniformly arranged indentations or dimples 33.
These dimples 33 may be either convex or concave. The dimples provide
stiffening properties to the front end of the probe cover to avoid stretching that
otherwise might occur pursuant to installation/use forces applied to sidewall 31.
In addition, the dimples make possible contact with the skin less critical, since
the contact area of the front end is reduced. Although Fig. 9 illustrates a probe
cover embodiment without a sill, a dimpled probe cover may also be provided
having a sill structure (not shown). This choice would depend on the actual
design of the infrared thermometer probe used.
Figs. 10-13 illustrate enlarged cross-section views of several variations of
a probe cover in accordance with the present invention having collar structure
that inc~udes a collarsible sill 14. In this design, forces for installing or using
the cover on sidewall 31 create compensating forces in collar 34 that prevent
film window stretch, and, in fact, cause the film window to collapse. For
example, Fig. 10 illustrates a probe cover having a membrane of varied
thickness whereby strain relief collar 34 is provided adjacent to thin wall 37,
which is connected to sidewall 31. As shown in the figure, when the cover is
positioned over probe 2, rim 11 of the probe engages with collar 34, as
illustrated by phantom lines 38. Due to the rigidity of collar 34, the forces
resulting from the interface of rim 11 of the probe with the cover, as shown by
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14
engaging force F, causes thin wall 37 to preferentially stretch, thus collapsingcollar 34 in direction 40, thereby resulting in centripetal force F2. In addition,
because the fulcrum point of collar 34, as shown by point c, is located outside
the direction of engaging force F, a torsion momentum is created within collar
34, causing a portion of the collar to move inward into position 39, as indicated
in the figure. As a result of collar 34 in conjunction with thin wall 37, sill 14
collapses toward optical axis 9 upon engagement of the cover with probe 2.
This insures a stretch-free film window.
As indicated, Fig. 11 illustrates another embodiment of a probe cover
having collapsing sill 14. The cover is positioned over probe 2 and engaged
with rim 11. Collar 34 comprises engagement fold 42 and fold angle ~ in
relation to optical axis 9. As shown in the figure, the probe 2 engages with thecover at a position 41 which causes rim 11 to move fold angle 42 into position
39, as indicated by the labelled thin line. As a result, centripetal force F2 iScreated and sill 14 is collapsed toward optical axis 9, thus preventing film
window 10 from being stretched. Experience indicates that the smaller the fold
angle a, the greater the centripetal force F2.
Fig. 11A illustrates a probe cover based on Fig. 11 and having thin wall
37 adjacent to sill 14. It should be noted that angle a, which is defined by rim11 at engagement point 41 and fold 42, results in an evident clockwise
collapsing of the sill 14 in direction 40, as indicated by the clockwise arrow,
thus, preventing film window 10 from being stretched. Similar to the
embodiment of Fig.11, the smaller the fold angle (a), the greater the centripetal
force that results when the cover is positioned onto the probe.
Continuing, Fig. 12 illustrates another embodiment of a probe cover
having a collapsing sill. As shown in Fig. 12, when the probe is placed into thecover, engagement fold 42 of collar 34 is engaged with rim 11 of the probe at
engagement point 41. This engagement c~uses fold 42 to unfold, creating
centrifugal force F1 outward from sill 14 and centripetal force F2 in the film
window in a direction towards optical axis 9. As shown in the figure, the
engagement position of probe 2 is indicated by phantom line 38 and fold 42 is
moved into position 39, as indicated by the labelled thin line. Accordingly, with
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this embodiment, the unfolding of fold 42 relieves any tension in film window 10and precludes s~retching.
Turning now to Fig. 13, a probe -over design is depicted that
corresponds closely to that of Fig. 12, DUt engagement fold 42 is placed outsideof sill 14 and makes contact on the periphery of rim 11, causing film window 10
to collapse as depicted by the ghost lines. The structure requires smaller
curvature of fold 42 which may simplify the manufacturing process.
Finally, the general probe cover design of Fig. 13 is depicted in Fig. 14A,
with an enlargement of collar 34 shown in Fig. 14B. As can be seen, collar 34
comprises fold 42 and sill 14 linking film window 10 to sidewall 31. The
sidewall 31 further comprises longitudinal ridges 80 for increasing wall stiffness
and permitting the use of a thinner and more elastic sidewall 31. Curves 70-72
are anchor points for attachment onto the IR probe (not shown).
It should be noted that in the embodiments shown in Figs. 10-13, any
centrifugal forces which could possibly be created in the front end portion whenthe cover is positioned over the probe would be converted to centripetal forces
in a direction towards the optical axis of the probe, thus providing strain relief in
the film window. It should also be pointed out that the various approaches
depicted in the individual figures can be combined as dictated by the particulardesign needs.
Attention is now directed to Figure 15A. In this embodiment, the cover
structure is very similar to that disclosed in Figures 1 and 14 showing a tapered
cone with an IR window at the forward end. According to this design, side wall
31 of the tapered cover has a variable thickness, gaining in thickness at the
base and becoming thinner at the tip of the cover. The slightly curved sidewall
31 has a radius that provides a thin air gap (thermal insulating) between the
cover and speculum, when installed. This probe cover design utilizes the
thickened base region as a more rigid structure to enhance attachment to the
probe itself via retention ears. In this way, the cover retention rim or "locking
groove" 71 engages the ears on the probe (or speculum) to positively retain the
cover with the window positioned over the speculum opening and wave guide,
as shown in the enlarged view of Fig. 15B. To accomplish this, referring now to
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16
Fig. 15C, the locking groove 71 must have an elastic hoop with diameter, Q,
that is able to stretch over the outer diameter, associated with the retention
ears. At the same time, the locking groove needs to have sufficiently tight
tolerances to prevent "play" after the cover is installed on the probe. This "play"
may otherwise contribute to vertical movement of the cover in response to
frictional forces on the cover sidewall, causing the cover to move downward on
the probe and engaging the probe tip into window 10.
To address this potential issue, the design depicted in Figure 15C
provides for a somewhat larger radius R, of curvature associated with locking
groove 71. In conjunction with the larger radius, the cover rim has a tighter
tolerance, and fits snugly up to retention ears of the probe with zero positive
clearance at planar positions 90 and 91. The slightly larger radius permits
engagement between the cover and retention ears with less force, while the
slightly tighter tolerance eliminates the "play" associ~ted with cover after it is
installed on the probe.
The foregoing arrangement may cause an airtight seal between the cover
and speculum via contact at rim 70. To prevent this, a pressure relief
arrangement is shown in Fig. 15A and provided by vent 88 and pocket 89,
placed at intervals (e.g., 90 degrees) around the perimeter of the
sidewall/locking groove.
Accomplishing the substantially rigid positioning of the cover on the
speculum requires selective control of the dimensions identified in Fig. 15C as
P, Q and R. In particular, by coordinating these dimensions with those of the
corresponding portion of the specu~um (depicted as segment 98, with retention
ears 95 in Figures 15A and 15B), two separate planes of contact are created,
90 and 91. However, the retention ears are spaced from the inner portion of
locking groove 71 and can pass the lower rim of the locking groove with a
minimal amount of insertion force. For select applica~ions, the enhanced
attachment described here may permit the use of a simpler IR window structure,
that is, a window with a flat surface absent the previously described collar
arrangement, but one that has a larger surface. This may be possible as the
CA 02251268 1998-10-13
WO 97/42475 PCT/US97/07509
17
retention means precludes the probe tip engagement that is otherwise
responsible for creating window stress.
Although the invention has been described in detail for the purpose of
illustration, it is to be understood that such detail is solely for that purpose and
5 that variations can be made therein by those skilled in the art without departing
from the spirit and scope of the invention.
