Toner level sensor

A toner level sensor for detecting the presence or absence or the level of residual amount of the toner of an electronic copier or the like. In order to secure stable operation regardless of changes of external environmental conditions such as temperature and humidity, a pair of transformers are provided with primary coils and secondary coils respectively wound on magnetic cores having a magnetic gap. When a magnetic member is present in the vicinity of a magnetic gap, the phases of the outputs of the secondary coils are opposite to each other, so that the differential output of the secondary coils is phase detected to determine the presence or absence of the residual toner amount or the level of residual amount.

BACKGROUND OF THE INVENTION 
The present invention relates to a toner level sensor for detecting the 
presence or absence or the level of residual amount of a toner for an 
electronic copier or the like, or more in particular to a toner level 
sensor which operates stably regardless of changes of external 
environmental conditions such as temperature or humidity. 
In conventional toner level sensors, as shown in FIG. 1, a transformer 8 
including a primary coil 2 and a secondary coil 3 wound on a magnetic core 
1 having a magnetic gap 20 is used, so that the output of the secondary 
coil 3 is positively fed back through an amplifier 4 thereby to form an 
oscillation loop. When a toner 5 having magnetism is located in the 
vicinity of the magnetic gap of the magnetic core 1, the coupling 
coefficient of the magnetic circuit changes with the level of residual 
amount of the toner, with the result that the feedback rate .beta. 
changes, and therefore the oscillation level changes as shown in FIG. 2. 
Thus, by adjusting and setting appropriately the coupling coefficient of 
the transformer 8 by a fine adjustment system (not shown), it is possible 
to identify and detect the level B with the residual amount of toner or 
the level A without any residual amount of toner. 
In the above-mentioned conventional toner level sensor shown in FIG. 1, 
however, the oscillation level should ideally change stepwise with 
.mu..beta.=1 as a boundary where .beta. is the amount of feedback and .mu. 
the amplification factor of an amplifier of the oscillation circuit. 
Actually, however, as shown by a solid line 6 in FIG. 2, the oscillation 
level rises gently and approaches a maximum value through an intermediate 
rise state. The intermediate state of this oscillation level is very 
sensitive to the external conditions such as temperature or humidity, and 
therefore a drift D is often caused as shown by a dashed line 6a and a 
dashed line 6b in FIG. 2. As a result, in the case where the detection of 
the toner level is set as A and B in FIG. 2 as mentioned above, such a 
disadvantage occurs that it may be utterly impossible to detect the toner 
level due to the change of feedback amount caused by the drift. 
This effect of drift may be avoided by adding a temperature compensating 
circuit, for instance, in which case the problem is an increased number of 
component parts. Another problem point is that since the causes of the 
change of the oscillation level at the intermediate state are complicated, 
full compensation therefor is very difficult in view of the product 
variations. 
SUMMARY OF THE INVENTION 
The object of the present invention is to obviate the above-mentioned 
problem points of the prior art and to provide a toner level sensor of 
novel construction which is capable of stable operation even under 
changing external environmental conditions such as temperature and 
humidity. 
In order to achieve the above-mentioned objects, the present invention is 
characterized by two transformers each including a primary coil and a 
secondary coil wound on a magnetic core having a magnetic gap, wherein 
when a magnetic material is present in the vicinity of the respective 
magnetic gaps, the phase of the output of the respective secondary coils 
are opposite to each other, so that the residual amount of toner is 
detected by phase detecting the differential output of the secondary 
coils. 
In the present invention, a greater effect is obtained if a magnetic 
material is arranged in the vicinity of the magnetic gap of the magnetic 
core of one transformer, so that a minus (or plus) phase detection output 
is produced in the absence of toner, while a phase detection output of 
opposite polarity is produced in the presence of toner of more than a 
predetermined amount. 
Also, in the present invention, forming the magnetic cores making up the 
above-mentioned two transformers as a common magnetic core or common 
magnetic cores which may be partly shared by the two transformers is 
effective for stabilization of operation. 
These and further objects, features and advantages of the present invention 
will become more obvious from the following description when taken in 
connection with the accompanying drawings wherein:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be described in detail below with reference to 
the drawings. 
FIG. 3 is a diagram schematically showing the construction of an embodiment 
of a toner level sensor according to the present invention. FIG. 4 is a 
diagram schematically showing another embodiment of the present invention. 
FIG. 5 is a diagram for explaining the operation of a toner level sensor 
according to the present invention shown in FIG. 4. FIG. 1 which is 
indicated to be the prior art shows the utilization of a C-shaped core. 
When a toner having a magnetism is located in the vicinity of the magnetic 
gap of the magnetic core 1, the coupling coefficient of the magnetic 
circuit changes with the level of residual amount of the toner. 
In the present invention, as illustrated in FIG. 3, two symmetrical 
C-shaped cores are provided each having a magnetic gap represented by 
reference numerals 21a and 21b. C-shaped magnetic cores 7a, 7b making up 
two transformers 9a, 9b and having magnetic gaps 21a, 21b are used 
respectively, and are wound respectively with primary coils L.sub.1a, 
L.sub.1b and secondary coils L.sub.2a, L.sub.2b. Also, coils L.sub.R1, 
L.sub.R2 are wound on the secondary side as reference signal detection 
coils. If the separate C-shaped cores of FIG. 3 are joined together a 
H-shaped core is provided having a common magnetic path portion as shown 
in FIG. 4. 
In FIGS. 3 and 4, the primary coils L.sub.1a, L.sub.1b are connected to the 
output terminal of an oscillator 10, and the secondary coils L.sub.2a, 
L.sub.2b and the reference signal detection coils L.sub.R1, L.sub.R2 are 
connected to the signal input terminal I.sub.1 and the reference signal 
input terminal I.sub.2 of a phase detector 11 respectively. The output O 
of the phase detector 11 is connected to be applied to a potential 
comparator 12. Further, an output signal from the phase detector 11 is 
compared with a reference voltage Vr corresponding to a preset toner level 
at a potential comparator 12, the output of which is adapted to drive a 
load 14 (such as a control circuit or display circuit) through a drive 
circuit 13. 
In the above-described toner level sensor according to the present 
invention, upon application of an oscillation output from the oscillator 
10 to the primary coils L.sub.1a, L.sub.1b, output signals corresponding 
to the degrees of coupling of the respective magnetic circuits made up of 
the two transformers 9a, 9b (FIG. 3) or a corresponding two transformer 
(FIG. 4) are induced in the secondary coils L.sub.2a, L.sub.2b. In the 
case where the degrees of coupling of the two magnetic circuits are equal 
to each other, the outputs of the secondary coils L.sub.2a, L.sub.2b are 
of opposite phases and cancel each other, so that the operation outputs 
thereof are reduced to 0 as shown in row a of FIG. 5. In the case where 
the toner remains, on the other hand, the degrees of coupling of the 
magnetic circuits are different from each other, and therefore the output 
of the magnetic circuit to which the toner is proximate is larger than the 
other. As a result the output difference is detected by the phase detector 
11 to produce a phase detection output corresponding to the phase 
involved. In this case, as shown in row b of FIG. 5, in order for a 
predetermined differential output to be produced, a magnetic member 15 may 
be arranged with respect to the magnetic gap of the magnetic circuits, so 
that the phase detection output is normally minus (or plus), while when 
the toner of more than a predetermined amount remains, a reverse output is 
produced by a toner 5 having magnetism as shown in row c of FIG. 5. This 
method may be more useful for level detection. 
As illustrated in row c of FIG. 5, a magnetic member 15 is arranged with 
respect to the magnetic gap of one of the magnetic circuits so that a 
minus (or plus) phase detection output is produced in the absence of 
toner, while a phase detection output of opposite polarity is produced in 
the presence of toner of more than a predetermined amount. In this manner, 
the coupling coefficient of the magnetic circuit having such magnetic 
member 15 arranged at the gap thereof is set to a value equivalent to the 
coupling coefficient exhibited when the toner level lies within a 
predetermined range and since the other magnetic circuit is arranged to 
have the coupling coefficient vary in proportion to the toner level, as 
shown in row b and c of FIG. 5, the phase detection output will be of one 
polarity when no magnetic toner 5 is present (row b) and will be of the 
opposite polarity when magnetic toner 5 of a sufficient level is present 
(row c). 
Referring again to FIG. 3, the oscillator 10 applies an AC current, for 
example, to each primary coil L.sub.1a and L.sub.1b of the magnetic cores 
7a and 7b of the magnetic circuits or transformers 9a and 9b. An AC output 
appears at each secondary coil (L.sub.2a, L.sub.2b) of the pair of 
transformers by this AC current. Further, since the secondary coils 
(L.sub.2a, L.sub.2b) are connected and have polarity as shown by the dot 
proximate thereto, the AC outputs at the secondary side are arranged to 
cancel each other with the difference or differential output being 
inputted to the phase detector 11 as represented by the input I.sub.1 
which is a difference signal. Since the magnetic cores having the magnetic 
gaps 21a and 21b are symmetrical in shape and size, when no magnetic 
material exists at either gap, the coupling coefficients of such magnetic 
cores and circuits are substantially the same. Additionally, the mutual 
inductance between each of the primary coils (L.sub.1a, L.sub.1b) and each 
of the secondary coils (L.sub.2a , L.sub.2b) is substantially the same 
value so that due to the connection of the secondary coils, the 
differential output is substantially zero. However, when magnetic toner 
level increases at the gap 21a of the magnetic core 7a of the transformer 
9a, the mutual inductance of the magnetic core 7a becomes larger than that 
of the magnetic core 7b and such value is represented in the differential 
output I.sub.1. 
In order to discriminate whether magnetic toner more than a predetermined 
level exists at the gap of the magnetic core 7a or not, a magnetic member 
15 is positioned at the magnetic gap of the magnetic core 7b of the 
transformer 9b so as to increase the coupling coefficient of the magnetic 
core 7b to a value corresponding to a predetermined level of the magnetic 
toner. Thus, when the coupling coefficient of the magnetic core 7a caused 
by magnetic toner existing at the gap of the magnetic core 7a is less than 
the increased part of the coupling coefficient of the magnetic core 7b, 
caused by the magnetic member 15, the output of the transformer 9b and the 
secondary coil is greater than that of the transformer 9a and conversely, 
when the magnetic toner level at the gap 21a increases to a level so as to 
have the coupling coefficient of the magnetic cores 7a be greater than the 
coupling coefficient of the magnetic core 7b, the output of the 
transformer 9a and the secondary coil thereof is larger than that of the 
transformer 9b. That is, when a level of magnetic toner more than the 
predetermined level is provided, a sine curve is outputted as the output 
I.sub.1 whereas, on the other hand, when the magnetic toner level is less 
than the predetermined level, a reversed sine curve shifted by .pi. is 
outputted as the output I.sub.1. Of course, the amplitude of the sine 
curve depends upon the extent of increase or decreases with respect to the 
predetermined level. The output I.sub.1 is supplied to a phase detector 
11. 
In order to effect a phase detection, such detection must be achieved with 
respect to a reference. Reference signal detection coils (L.sub.R1, 
L.sub.R2) are provided, as illustrated in FIG. 3, and are wound on the 
secondary side of each magnetic core with the coils being connected and 
having the same polarity as shown by the dot proximate thereto and the 
output I.sub.2, which is a sum signal is obtained therefrom and supplied 
to the phase detector. While, as pointed out above, the phase of the 
differential output I.sub.1 changes by the level of the magnetic toner, 
the phase of the reference output I.sub.2 does not change in dependence 
thereon. Accordingly, the phase detector detects the phase between such 
outputs and provides a output indicative thereof to the potential 
comparator 12 wherein it is compared with a reference voltage V.sub.r and 
utilized to drive a drive circuit in accordance with the difference 
therebetween. The operation of the phase detector will be explained 
referring FIG. 6-FIG. 14. Referring to FIG. 6, the output of the secondary 
coil (L.sub.2a) of the transformer 9a varies in accordance with the level 
of the magnetic toner, i.e., large toner level, medium toner level and no 
toner. On the other hand, the output of the secondary coil (L.sub.2a) of 
the transformer 9b is constant since the magnetic member 15 is arranged at 
the gap thereof as shown in FIG. 7. Consequently, the total output of the 
secondary coils is shown in FIG. 8. When the total output is compared with 
a threshold value (that is only a positive value) the total output I.sub.1 
is as shown as the A signal in FIG. 9. On the other hand, the signal at 
the reference signal detection coil (L.sub.R1, L.sub.R2) due to the 
connection of such coils is shifted by 180 degrees or is the reverse of 
the sine curve in FIG. 8(a) with this signal being shown in FIG. 10. When 
this signal is compared with a positive threshold value the result is 
shown in FIG. 11. 
The phase detector operates to compare the phases of the signals input 
thereto and such may be accomplished by an Exclusive OR operation as well 
be explained in the following. 
The signal (A signal) as determined by the threshold of the differential 
output I.sub.1 is shown in FIG. 12 for the different levels of toner. The 
signal (B signal) of the reference output I.sub.2 is shown in reference 
FIG. 13. Based upon an Exclusive OR operation of such signals, the signal 
values FIG. 14 are obtained as shown in by the phase detector 11. The thus 
obtained signal can be rectified, for example, by a low pass filter 
provided in the last stage of the phase detector, and changed to a DC 
current level as represented by the phase detection outputs of FIG. 5 row 
b and row c. Thereafter, the amplitude of the output of the phase detector 
is compared with the reference voltage V.sub.r by means of the potential 
comparator 12 and the output thereof is supplied to a drive circuit 13 so 
as to control the toner supply, for example. 
As described in detail above, according to the present invention, the 
residual amount of toner is detected by comparing the output signals of a 
couple of magnetic circuits, and therefore a highly accurate detection is 
possible without being substantially affected by changes of such external 
environmental conditions as temperature and humidity, thus producing a 
very high industrial advantage. 
While we have shown and described various embodiments in accordance with 
the present invention, it is understood that the same is not limited 
thereto but is susceptible of numerous changes and modifications as known 
to those skilled in the art and we therefore do not wish to be limited to 
the details shown and described herein but intend to cover all such 
changes and modifications as are encompassed by the scope of the appended 
claims.