Apparatus intended for classifying the quantity of a fatty product found on the skin surface

Measurements of the greasiness of skin are made by applying a plate against a region of skin to be studied and then inserting the plate in a recess of the casing, in register with a photodiode and a phototransistor. A series of n (in this case 5) indicator lamps is connected to a set of n-1 (in this case 4) comparators each comparing a respective voltage threshold level with the voltage delivered by the photoresistor, so that the voltage of the transistor, and hence the greasiness of the deposit on the plate through which luminous flux from the photodiode to the phototransistor passes by reflection from the upper side of the plate, can be determined by observing which lamps are illuminated.

DESCRIPTION 
The present invention relates to an apparatus to be used for determining 
the quantity of a fatty or greasy product, for instance of sebum, found on 
the skin surface of a living subject. This determination is effected by 
means of signal lamps which light up selectively according to the quantity 
of sebum found in one or other of a multiplicity of predetermined classes. 
In U.S. patent application Ser. No. 844,038 (now abandoned to the benefit 
of the two Continuation-In-Part Applications Ser. No. 27,718 and Ser. No. 
27,717) there has already been described an apparatus to be used for 
determining the quantity of sebum secreted by a skin, on the basis of 
measuring an optical characteristic of a specimen. In the said U.S. patent 
application Ser. No. 844,038 a luminous flux modulated at a fixed 
frequency is directed on to a plate having a ground surface, which plate 
has previously been applied in a predetermined way to a region of skin to 
be examined, and the flux emanating from the plate is measured by a flux 
receiver which only takes account of luminous flux having the particular 
frequency modulation of the transmitter. From this received flux "data" it 
is possible to deduce the data elements for determining the sebum 
secretion of the skin region against which the ground-surfaced plate has 
been applied. In a variant of this apparatus, the ground glass plate 
comprises a reflecting rear side, so luminous emission of a photodiode is 
directed onto the said plate and is reflected towards a phototransistor 
whose output provides a measurement of the quantity of sebum secreted by 
the skin. The measurement thus obtained is independent of the external 
light conditions by reason of the modulation of the luminous flux. This 
device gives every satisfaction, but has the drawback of being relatively 
expensive taking into account the electronic circuit which is necessarily 
associated with the emitter photodiode and the receiver phototransistor. 
In British Patent Application No. 2022818A there has also been proposed a 
simple design of apparatus for determining the sebum quantity secreted by 
a skin region. In this apparatus, the casing contains inside a light 
emitter supplying a continuous luminous flux towards a sight which carries 
at least one mark or scale capable of being positioned within the casing 
opposite the translucent element on which the sebum of the skin region to 
be examined has been deposited. The evaluation of the sebum quantity is 
effected by observing the aforementioned mark through the abovementioned 
translucent element. This device is fairly cheap but gives results which 
essentially depend on the visual evaluation made by the user. 
The object of the present invention is to provide apparatus to be used for 
determining the quantity of fatty products carried by a skin, the said 
apparatus being capable of inexpensive manufacture but nevertheless making 
it possible to dispense with any need for visual evaluation by the user. 
Thus the apparatus according to the invention has the advantage that it 
can be used by any user, even an unskilled user, to give uniform results 
in all cases, this advantage being obtained whilst maintaining a moderate 
cost. The apparatus according to the invention may in particular be used 
for (a) determining the quantity of sebum secreted by the skin or for (b) 
determining the quantity of oil remaining, after a certain time, on a skin 
which after the application of the said oil has absorbed a proportion 
thereof. 
Accordingly the present invention provides apparatus to be used for the 
classification of the skin of a living subject into n predetermined 
classes where n is an integer greater than one, the said classification 
being effected according to the quantity of product carried by the said 
skin, such apparatus comprising: a translucent element having two surfaces 
of which one surface is to be applied in a predetermined way on skin to be 
examined; a luminous flux emitter arranged to irradiate said translucent 
element; a luminous flux receiver positioned to receive luminous flux from 
said irradiated translucent element; and means for comparing the output of 
the flux receiver with (n-1) predetermined threshold values to produce a 
display of at least one of n possible luminous indications representing 
the abovementioned n classes. 
The apparatus according to the invention allows the skin examined to be 
classified in a certain number of predetermined categories, this 
classification being automatically effected by the lighting up of light 
signals, each one of which corresponds to a predetermined skin category. 
In a preferred embodiment, the flux emitter may be designed to emit a 
continuous flux; the translucent element may be a ground-surfaced plate of 
which the side which does not receive the luminous flux constitutes a 
plane mirror; the ground-surfaced plate may, in particular, be made of 
glass, of a plastic material, or of sapphire; the flux emitter may be a 
photodiode; the flux receiver may be a phototransistor; the output voltage 
supplied by the phototransistor receiver may be forwarded in parallel to 
(n-1) comparators, each one of which receives on its other input a 
respective one of several predetermined threshold voltages; the ground 
plate constituting the translucent element may be arranged opposite the 
flux emitter and receiver and be held longitudinally in guides of a casing 
of the apparatus and cooperate, by that one of its edges which are 
perpendicular to the guides which is first introduced into the said 
guides, with a switch controlling the electric supply of the flux emitter. 
In a first variant of the apparatus according to the invention, the outputs 
of the (n-1) comparators are interconnected in parallel on the same line 
and are separated from each other by at least one photodiode, each one of 
the n skin classes being associated with a respective photodiode 
constituting a signal lamp; the line interconnecting the output of the 
comparators may be connected by its two end terminals to the opposite 
polarities of the electricity supply, at least one photodiode being 
provided between each terminal and the adjacent comparator; a safety diode 
may be placed in series with the photodiode constituting the signal lamp 
between the terminal connected to the positive lead and the output of the 
adjacent comparator. 
In a second variant of the embodiment of the apparatus according to the 
invention, each one of the (n-1) comparators is connected to a decoder 
assembly whose output feeds a display unit capable of displaying a number 
taken from a set of n numbers, each one of which numbers is assigned to a 
respective one of the predetermined n skin classes; the decoder assembly 
may be constituted by a multiplicity of logic gates and may forward a 
binary code signal to the display unit. 
In a third variant of the embodiment of the apparatus according to the 
invention, the output of the receiver phototransistor is connected to the 
frame by a parallel pair comprising on the one hand a resistor at the 
terminal at which the voltage which is applied to the (n-1) comparators is 
taken, and on the other hand a capacitor; in this way, the voltage 
supplied by the photoreceiver to the comparator inputs is established with 
a progressiveness according to the capacitance of the capacitor and the 
changeover of the outputs of those of the comparators which have to change 
in view of the final value attained by the output voltage of the 
photoreceiver, is effected with a time shift; the outputs of the (n-1) 
comparators are connected in parallel to the input of the read-out device, 
the said read-out device comprising a pulse counter capable of supplying a 
numerical display according to the number of pulses received; the output 
of each one of the comparators is provided with a circuit transforming a 
change in voltage level into a pulse and with an insulating diode. 
It has been found that the apparatus according to the invention has made it 
possible to effect the classification of an examined skin region very 
satisfactorily into a number of predetermined classes. In fact, it is 
known that there exists a good correlation between the transparence of, on 
the other hand, a ground strip applied beforehand for some time and with a 
given pressure to the skin region to be examined, and on the other hand 
the quantity of the fatty products deposited on the said strip. In 
dependence on the transparence of the ground strip subjected to 
examination in the apparatus according to the invention, one or other of 
the signal lamps of the apparatus lights up which determines the class of 
the examined skin without the need for assessment by the user of the 
apparatus. Moreover, the emission of the photodiode used as the flux 
emitter is not subject to ageing, and the response of the apparatus is 
therefore constant in respect to time.

Referring to the drawing, it will be seen that the casing of the apparatus 
according to the invention as a whole has been designated as 1. Casing 1 
has a parallelpiped shape and has on one of its edges a recess 2 having a 
substantially rectangular plan view. Recess 2 comprises on its two 
longitudinal edges guides 3 which slidably receive the longitudinal edges 
of a plate 4 having a ground surface, in this case a ground glass plate. 
Plate 4 comprises a metallised side 4a which constitutes a plane mirror 
and it is intended to slide in the guides 3 so as to be received in the 
recess 2. When plate 4 is thus positioned in the casing 1, its front 
transverse edge 4b cooperates with the moving contact of a switch 5 so 
that, when the plate 4 is pushed home in the recess 2, switch 5 is closed 
whereas on the contrary when this pressure is not effected the switch 5 
remains in an open position. 
The apparatus described is intended to be used for classifying the various 
skin regions presented to the user of the apparatus into appropriate ones 
of five categories, from the point of view of their sebum secretion. This 
classification is based on the fact that a strip of ground glass, such as 
strip 4, has a degree of transparence varying according to the quantity of 
sebum which is disposed on its non-metallised side. The user thus needs to 
apply such a plate 4 during a given time and with a given pressure against 
the skin region to be examined and it is known that in this case, the 
quantity of sebum deposited on plate 4 is the greater, the greater the 
secretion of the skin region being investigated. In other words, the 
greater the secretion of sebum of the skin region examined, the more 
transparent the plate 4 becomes. Hence, all that is necessary is to 
determine the transparence of plate 4 in order to define the "greasiness" 
class of the skin region being examined. 
The principle of the apparatus according to the invention lies in directing 
a monochromatic luminous flux from a photodiode 6 on to the ground side of 
plate 4 and recovering this luminous flux after passage one way through 
the thickness of plate 4, then reflection at the metallised surface 4a and 
finally, a return passage through the thickness of plate 4 on to the base 
of a phototransistor 7 which has an output voltage substantially 
proportional to the luminous flux received. The distances on the one hand 
between photodiode 6 and the plate 4, and on the other hand between the 
plate 4 and the phototransistor 7 are clearly determined since precise 
positioning of plate 4 within housing 2 is ensured by means of guides 3 
and since the photodiode 6 and photoresistor 7 are arranged at the bottom 
of recess 2. In these circumstances, there exists a relation between the 
quantity q of the sebum deposited on plate 4 (expressed in .mu.g/cm.sup.2) 
and the voltage V expressed in mV at the output of phototransistor 7. The 
curve representing the variation of V as a function of q is given in FIG. 
2; of course, this curve presupposes a given level for the luminous 
emission of photodiode 6. 
Using the apparatus described, the various skin regions which may be 
submitted for examination are to be classified into five distinct 
categories. To do this, four category limits are defined, corresponding to 
four values of the quantity of sebum deposited on plate 4 during one 
application operation on the skin according to the adopted procedure 
(using a constant predetermined time of application and pressure of 
application). 
The abovementioned four limits have been represented in FIG. 2 as 
corresponding respectively to 50, 100, 150 and 220 microgrammes of sebum 
per cm.sup.2 of the plate 4. Each one of these limits corresponds to the 
output voltages V.sub.1, V.sub.2, V.sub.3, V.sub.4 of the phototransistor 
7. The first skin category is that in respect of which the sebum deposit 
is below 50 microgrammes per cm.sup.2 ; for this category, the output 
voltage of the phototransistor is between V.sub.0 and V.sub.1 ; for the 
second category, the sebum quantity is between 50 and 100 microgrammes per 
cm.sup.2 and the output voltage of the phototransistor 7 is between 
V.sub.1 and V.sub.2 ; for the third category, the sebum quantity is 
between 100 and 150 microgrammes per cm.sup.2 and the voltage between 
V.sub.2 and V.sub.3 ; for the fourth category, the sebum quantity is 
comprised between 150 and 220 microgrammes per cm.sup.2 and the voltage is 
between V.sub.3 and V.sub.4 ; and for the fifth category, the sebum 
quantity exceeds 220 microgrammes per cm.sup.2 and the voltage is higher 
than V.sub.4. 
The electronic circuit of a first variant of the apparatus according to the 
invention is schematically represented in FIG. 3. It will be seen that 
this circuit is energised by a battery 8 giving a 9 volt voltage supply. 
Switch 5 is in series with battery 8 to control supply to the emitter 
photodiode 6 via an adjustable resistor 9. Phototransistor 7 receives on 
its base the luminous emission transmitted by the plate 4. The voltage of 
the battery 8 is applied to the emitter of phototransistor 7 and the 
collector is connected to the frame via a resistor 10. The output voltage 
V of the phototransistor 7 is the voltage at the terminals of resistor 10 
which thus serves to adjust the sensitivity of the apparatus. 
The output voltage of phototransistor 7 is applied to the positive inputs 
of four comparators 11a, 11b, 11c and 11d. The negative inputs of these 
same four comparators are connected to the electric supply and to the 
frame via resistors 12, 13, 14, 15 and 16 which together define a 
multi-step potential divider. The resistor 12 is interposed between the 
positive lead and the negative terminal of comparator 11a; the resistor 13 
is interposed between the negative terminals of the comparators 11a and 
11b; the resistor 14 is interposed between the negative terminals of the 
comparators 11b and 11c; the resistor 15 is interposed between the 
negative terminals of the comparators 11c and 11d; and the resistor 16 is 
interposed between the negative terminal of comparator 11d and the frame. 
The outputs of the four comparators 11a, 11b, 11c and 11d are connected in 
parallel on a line which is established between the positive lead and the 
frame and comprises a given number of diodes. A first photodiode 17 is 
connected between comparator 11a and the frame; photodiode 18 and a safety 
diode 19 are connected between the comparator 11d and the positive lead, 
(the safety diode 19 being disposed between the output of comparator 11d 
and the photodiode 18); and photodiodes 20, 21 and 22, respectively, are 
interposed between the comparators 11a-11b, 11b-11c, and 11c-11d. The 
photodiodes 18, 22, 21, 20 and 17 of this set constitute the five signal 
lamps of the apparatus and are intended to indicate to the user that the 
skin region examined corresponds to the particular one of the five 
predetermined classes pertinent to the signal lamp which illuminates. The 
abovementioned five signal lamps therefore appear along one of the edges 
of casing 1 of the apparatus; the corresponding photodiodes have a current 
limiting resistor incorporated to conserve the energy of battery 8. 
The functioning of the device which has been described above is easy to 
explain: the user, having applied plate 4 against the skin region to be 
examined, arranges this plate in the recess 2 of the apparatus and pushes 
the plate 4 to the end of the recess to actuate switch 5 (FIGS. 1 and 3). 
When switch 5 is closed, photodiode 6 emits a continuous luminous flux 
which passes through the plate 4, is reflected on metallised surface 4a, 
returns through the plate 4 and is received on the base of phototransistor 
7. The voltage thus obtained at the output of the phototransistor 7 is 
applied to the positive inputs of the four comparators 11a, 11b, 11c and 
11d. 
If there is a low output voltage, that is to say a small quantity of sebum 
has been deposited on plate 4, the voltage on the positive input of 
comparator 11d is below the reference voltage on its negative input 
(determined by the values of the resistors 12, 13, 14, 15, 16). In that 
case, the output of comparator 11d is at zero and photodiode 18 lights up 
whereas the photodiodes 17, 20, 21 and 22 remain extinguished. If the 
quantity of sebum on plate 4 is increased sufficiently, the output voltage 
of the phototransistor 7 is increased and attains the higher reference 
voltage obtained on the negative terminal of comparator 11d. At this 
instant, the comparator 11d changes over and supplies a voltage of 
(9-.epsilon.) volts on its output, where .epsilon. corresponds to the drop 
in the internal voltage of the comparator. Photodiode 18 is extinguished 
while, on the other hand, photodiode 22 lights up; however, the other 
photodiodes remain extinguished. To allow for the case where .epsilon. may 
have a value higher than the voltage drop in the photodiodes used, there 
has been added in series with photodiode 18, a safety diode 19 which makes 
it possible to ensure the definite extinction of photodiode 18 at the time 
when comparator 11d changes over. 
If the quantity of sebum on plate 4 is increased still further, the output 
voltage of phototransistor 7 increases to attain a value equal to the 
voltage applied to the negative terminal of comparator 11c. In this case, 
comparator 11c changes over, causing photodiode 22 to be extinguished and 
photodiode 21 to be illuminated. In this case, there is no risk of 
photodiode 22 remaining illuminated because the comparators 11c and 11d 
are identical and therefore have the same internal voltage drop. It will 
therefore be seen that as the quantity of sebum on plate 4 increases, 
lighting up of firstly the photodiode 21, then photodiode 20 and finally 
photodiode 17, for the highest quantity of sebum occurs. No two 
photodiodes remain illuminated simultaneously. Thus a single photodiode is 
illuminated to correspond to a skin category defined by the limits 0, 50, 
100, 150, 220 microgrammes per cm.sup.2 specifically set out in FIG. 2. 
It should be noted that the presence of the adjustable resistor 9 allows 
for any production tolerances of the photodiode 6 and the phototransistor 
7 to be compensated, so the apparatus according to the invention may be 
accurately adjusted in spite of the production tolerances obtaining in the 
case of the electronic components used. 
FIG. 4 partly represents the electronic circuit corresponding to a second 
variant of the embodiment of the apparatus according to the invention. 
FIG. 4 only shows the part of the circuit which is downstream of the 
photoreceiver 7, the part that is upstream being strictly identical to 
that represented in FIG. 3. In the circuit of FIG. 4, the elements which 
are identical with those described in the first variant, for example the 
photoreceiver 7 and its associated resistor 10, have been designated by 
the same reference numbers. The voltage at the terminal connecting the 
photoreceiver 7 to the resistor 10 is applied to the positive inputs of 
comparators 11a, 11b, 11c and 11d. The negative inputs of these 
comparators are supplied with reference voltage values defined by 
resistors 12, 13, 14, 15 and 16. The whole part of this circuit is 
identical with the corresponding one in the first variant. 
In this second variant, however, the outputs of the four comparators are 
applied to a decoder unit 31. It is clear that each comparator output is, 
according to the output voltage of photoreceiver 7, either at zero level 
or at level 1, so that for each measurement effected by the apparatus 
according to the invention the decoder unit 31 is receiving a code 
corresponding to that indicated in the table below. In this Table, S 
denotes the output voltage at the terminals of the resistor 10, and S1, 
S2, S3 and S4 respectively denote the threshold voltage values relating to 
the comparators 11d, 11c, 11b and 11a and defined by the set of the 
resistors 12, 13, 14, 15 and 16. When voltage S is below the value of S1, 
the outputs of all the comparators are at zero; when voltage S reaches the 
value S1, the comparator 11d changes over and delivers at its output a 
voltage equal to the supply voltage less the internal voltage drop of the 
comparator 11d, this value being considered as corresponding to level 1. 
The Table below gives in its second column the output states of the four 
comparators depending on the value of voltage S in relation to the four 
thresholds S1, S2, S3, S4 (indicated in the first column). 
______________________________________ 
Binary 
code 
Output levels 
Sebum supplied 
Display 
of the deposits by on 
Value comparators on plate decoder 
Device 
of S 11d 11c 11b 11a 
4 31 30 
______________________________________ 
S .ltoreq. S1 
0 0 0 0 from 0 to 000 0 
50 .mu.g/cm.sup.2 
S1 &lt; S .ltoreq. S2 
1 0 0 0 from 50 to 
001 1 
100 .mu.g/cm.sup.2 
S2 &lt; S .ltoreq. S3 
1 1 0 0 from 100 to 
010 2 
150 .mu.g/cm.sup.2 
S3 &lt; S .ltoreq. S4 
1 1 1 0 from 150 to 
011 3 
220 .mu.g/cm.sup.2 
S4 &lt; S 1 1 1 1 exceeding 100 4 
220 .mu.g/cm.sup.2 
______________________________________ 
The four threshold values S1, S2, S3, S4 define five possible states 
corresponding to the quantities of sebum applied to the ground-surfaced 
plate 4 of the apparatus; these stages being the same as those defined for 
the first variant of the embodiment previously described. The quantities 
of sebum corresponding to these five classes are indicated in the third 
column of the above Table. The decoder unit 31 is constituted by an 
assembly of logic gates which, on receipt of the codes indicated in the 
second column of the Table above, supplies at its output the binary codes 
indicated in the fourth column of the Table above. These three figure 
binary codes are directed to a read-out device 30 which displays the 
decimal number corresponding to the binary code received. The decimal 
number in question is indicated in the fifth column of the Table above. It 
will thus be seen that this second variant makes it possible to display, 
on a screen, the number of the skin class corresponding to the deposit of 
sebum effected on the ground-surfaced plate by the skin region under 
examination by the apparatus according to the invention. This mode of 
display may, in certain cases, be preferable to the lighting up of one of 
a series of photodiodes. 
In FIG. 5, there is represented a third variant of the electronic circuit 
of the apparatus according to the invention; this representation has been 
effected as a partial representation and (like FIG. 4) relates only to the 
components downstream of photoreceiver 7; the circuit upstream of the said 
photoreceiver being strictly identical with that which has been described 
in detail with regard to the first variant and shown in FIG. 3. In this 
third variant, several components are strictly identical with those used 
in the first variant and these components (such as photoreceiver 7 with 
its emitter connected to the frame via a resistor 10 and having the 
voltage at a point between the photoreceiver and the resistor applied to 
the positive terminals of four comparators 11a, 11b, 11c, 11d) have been 
designated by the same reference numbers as in the first variant. As in 
FIG. 3, the negative terminals of the four comparators receive the voltage 
threshold values defined by the resistors 12, 13, 14, 15 and 16. 
In the first variant, when the ground-surfaced plate 4 is placed in 
position in the apparatus, the photoreceiver 7 receives on its base a 
quantity of light and delivers at its emitter a voltage which is 
instantaneously established at the value corresponding to the quantity of 
sebum carried by the ground-surfaced plate 4 under examination. 
In the third variant, shown in FIG. 5, an attempt has been made to spread 
out in time the voltage rise of the emitter of the photoreceiver; to do 
this, provision has been made for a 10 micro-farad capacitor 41 to be 
connected in parallel with the resistor 10. In this way, the rise in 
voltage at the positive terminals of the four comparators 11a, 11b, 11c, 
11d is effected gradually from zero up to the maximum value S 
corresponding to the quantity of sebum deposited on the plate 4 under 
examination. According to the position of value S in relation to the four 
threshold voltage values S1, S2, S3 and S4 relating to the four 
comparators 11d, 11c, 11b and 11a, as the voltage on the emitter of 
photoreceiver 7 is being established, none of the comparator outputs will 
change over if value S is below all the threshold values, or the four 
outputs of the four comparators will successively change over if value S 
is higher than all the threshold values, or a certain number of the 
comparators will successively change over if value S is an intermediate 
value between the two abovementioned extreme cases. 
At the output of each of the comparators, there has been arranged a 
respective circuit 42 supplying a pulse at its output at the instant when 
its input is subjected to the rising front corresponding to the 
change-over of the associated comparator. Such a circuit 42 is of a known 
form, constituted by a capacitor whose output is connected to the frame 
via a resistor. The output of each of the four circuits 42 is provided 
with an insulating diode 43 and is fed to the single input of a pulse 
counter 40. It is clear that, according to the value of voltage S, the 
pulse counter 40 will receive a different number of pulses corresponding 
to the number of comparators whose outputs have changed over. Spreading 
out the voltage rise of the emitter of photoreceiver 7 makes it possible 
to separate in time the pulses corresponding to the change-over of the 
comparators. The pulse counter 40 makes it possible to display, on a 
screen, a numerical indication corresponding to the number of pulses 
received. Such a counter is well known in the art and is, for instance, 
marketed under reference "TIL 306" by the "TEXAS INSTRUMENTS" Company. It 
will thus be seen that this third variant again provides for a numerical 
display corresponding to the number allotted to the skin category whose 
sebum secretion is subjected to examination. 
It is clear that the apparatus which has been described may be extremely 
moderately priced and may be made very compact in size. Moreover, the 
determination effected by this apparatus is totally independent of the 
user's faculties of observation.