Method and apparatus for detecting residual quantity of toner in image forming device

An image forming apparatus includes a developing unit and a photoconductive drum. A toner sensor is disposed in a toner mixing chamber of the developing unit. A mixing member is included in the chamber for mixing and frictionally charging the toner. A detection device is mounted on the unit for detecting the residual quantity of density of the toner according to the output voltage of the sensor. The residual quantity or density of the toner is detected by sampling an output voltage of the toner sensor at predetermined times during a predetermined period while the mixing member is rotated at a specific constant speed, and averaging the sampled vales. As a result correct data for the residual quantity or density of the toner can be obtained.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a method and apparatus for detecting the residual 
quantity of toner in an image forming device, and particularly to a method 
and apparatus for detecting the amount of toner in image forming devices 
such as electrophotographic printers and copy machines in which the toner 
is mixed by a mixing member during the printing operation. 
2. Description of the Related Art 
Generally, in image forming devices such as electrophotographic printers, 
copy machines and fax machines, an electrostatic latent image 
corresponding to an image to be printed or copied is optically formed on a 
photoconductor drum. The latent image is then developed with a toner into 
a toner image, which is transferred to and fixed on a recording sheet to 
complete the printing or copying operation. As the printing or copying 
operation is repeated, the toner is gradually consumed. When the toner is 
reduced below certain level, the printed or copied image becomes thinned 
out so as to provide an unclear printed or copied image. It is usual, 
therefore, to detect the residual quantity or density of the toner using a 
toner sensor disposed at a toner mixing chamber wherein a mixing member is 
turned for mixing and frictionally charging the toner. The toner sensor 
detects the residual quantity or density of the toner mixture and provides 
an output voltage in accordance with the amount of the toner. 
Usually, the image forming device is equipped with at least one toner 
indicator for indicating a need for replenishment of the toner or 
replacement of a toner container. When the quantity or density of the 
toner drops below a specified value, the toner indicator is actuated to 
inform the user to replenish the toner or replace the toner container. 
FIG. 1 is a cross-sectional view of a conventional developing unit of the 
sort often employed for electrophotographic printers etc. As seen in FIG. 
1, the unit includes a developing unit 1, and a photoconductor drum 2. The 
developing unit 1 has a mixing chamber 10 where the toner 9 is mixed and 
charged by friction, a toner separating portion 20, and a toner sensor 30. 
A toner mixing member 11 is mounted in chamber 10 for stirring and 
frictionally charging the toner 9. The toner 9 is fed to a magnet roll 21 
of the toner separating portion 20. As magnet roll 21 is rotated, the 
toner 9 is carried on the surface thereof. The thickness of the toner on 
the roll 21 is regulated by a doctor blade 22. The toner then comes into 
contact with the surface of the photoconductor drum 2 facing the magnet 
roll. A bias voltage is applied to the magnet roll 21 and the toner is 
transferred onto a electrostatic latent image formed on the surface of the 
photoconductor drum to thereby form a toner image according to the 
difference between the bias voltage and the surface potential of drum 2. 
FIG. 2 is a perspective view illustrating the mixing member 11 of FIG. 1. 
Mixing member 11 includes a rotational shaft 11c which carries four arms 
11a. Two of the arms 11a are mounted on the same side of the shaft 11c and 
the other two arms 11a are mounted on the opposite side thereof. The free 
ends of the arms 11a are connected by two bars 11b. 
As shown in FIG. 3, toner sensor 30 is attached to the toner container 12 
so as to detect the residual quantity or density of the toner in chamber 
10. As shown in FIG. 4 toner sensor 30 comprises a differential 
transformer having a drive coil L1, a reference coil L2, and a detection 
coil L3. These coils L1, L2 and L3 are wound around the same core 31. A 
high-frequency signal of 500 KHz is applied to the drive coil L1 from an 
oscillator OSC. 
There are two types of developers for image forming device. One type is a 
single component developer consisting only of the toner, and the other 
types is a two-component developer which contains the tone and a magnetic 
carrier such as ferrite or iron. Recently, a new type of two-component 
developer has become known, wherein the rate of usage of the carrier is 
very small as compared with the rate of usage of the toner. This new type 
of two-component developer is sometimes referred to as a 1.5 component 
developer. 
When a two-component developer which is a mixture of magnetic carrier and 
the nonmagnetic toner is used, when the relative amount of the toner is 
high in a given volume, the relative amount of the magnetic carrier 
substances to too low to cause an increase in the magnetic resistance of 
the developer. On the other hand, if the relative amount of the toner 
becomes lower in the same volume, the relative amount of the carrier 
increases so as to reduce the magnetic resistance. The output voltage of 
the detection coil L3 changes in response to the relative amount (density) 
of the toner in the mixture, and the output voltage Vo of the toner sensor 
changes accordingly. Thus, the density of the toner is detachable 
according to the output voltage Vo of the toner sensor 30. 
When the 1.5 component developer, which is a mixture of a small quantity of 
magnetic carrier and a large quantity of the nonmagnetic toner is used, 
the toner sensor 30 cannot detect the density of the toner. However, as 
the toner is consumed, the magnetic resistance of the developer changes 
depending on whether the developer is above, below, or around the surface 
of the toner sensor. Accordingly, the residual quantity of toner in the 
chamber 10 is detectable according to the output Vo of the toner sensor 
30. 
While the toner sensor 30 is detecting the residual quantity of the toner 
9, the toner 9 is being stirred and moved by the mixing member 11. The 
output voltage Vo of the toner sensor 30, therefore, oscillates as shown 
in FIG. 5 as the mixing member 11 rotates. As shown in FIG. 5, the mixing 
member 11 starts to rotate at time t1, the rotational speed thereof 
becomes constant after time t2, and the printing operation of the image 
forming device is carried out between time t2 and t3. The rotational speed 
of the mixing member 11 decreases after time t3, and the mixing member 11 
stops at time t4. 
The amplitude of the output voltage Vo of the toner sensor 30 as a function 
of the acceleration or deceleration of the rotation of the mixing member 
11. When the mixing member 11 ceases to rotate, the output voltage Vo of 
the toner sensor 30 indicates a high or low value. In a case where the 
mixing member 11 stops moving at a point where a large quantity of the 
toner 9 is disposed on the toner sensor 30, the output voltage Vo of the 
toner sensor 30 will be high. This condition is indicated by dot and 
dashed lines A in FIG. 3. If the mixing member 11 should stop just after 
passing over the toner sensor 30, the output voltage Vo of the toner 
sensor 30 will be low because the quantity of the toner 9 on the toner 
sensor 30 will have been reduced by the mixing member 11. This condition 
is indicated by the phantom lines B in FIG. 3. 
In this way, the relationship between the toner 9 and the toner sensor 30 
changes according to the rotational position of the mixing member 11. In 
conventional devices, the conditions described destabilize the output 
voltage of the toner sensor 30 and cause an incorrect detection of the 
residual quantity of the toner. 
When detecting the density of the toner 9, the output voltage Vo of the 
toner sensor 30 also fluctuates depending upon the rotation of the mixing 
member 11. Thus, the output voltage Vo becomes larger or smaller depending 
on the stopping position of the mixing member 11, and therefore, the 
density of the toner 9 is not correctly detected. 
SUMMARY OF THE INVENTION 
An object of the invention is, therefore, to provide a tone quantity 
detecting method that correctly detects the residual quantity or density 
of toner. 
According to the present invention, the output voltage of the toner sensor 
30 is sampled at predetermined time periods after the rotational speed of 
the mixing member becomes constant. The average of the sampled values 
provides data which relates to the residual quantity or density of the 
toner. The predetermined number of sampled values taken during a certain 
time period may be substantially equal to a random number times the 
rotational period of the mixing member 11. 
When the rotational speed of the mixing member 11 becomes constant, the 
output voltage Vo of the toner sensor 30 provides a regular waveform. In 
this condition, sampling of the output voltage of the toner sensor 30 is 
carried out at predetermined times during a predetermined period according 
to the present invention, and the sampled values are averaged to provide 
data which relates to the residual quantity or density of the toner. In 
this way, according to the present invention, the residual quantity or 
density of the toner is determined without being influenced by the 
stopping position of the mixing member 11. 
When the residual quantity or density of the toner is sampled only after 
the mixing member 11 has reached a specific constant speed, clods of toner 
are separated into particles and toner sticking to walls is removed, so 
that the residual quantity and density of the toner may be more stably 
detected. The average of the sampled values of the output voltage of the 
sensor over a period of time that is a random number times the rotational 
period of the mixing member provides data relating to the residual 
quantity or density of the toner. The output voltage of the toner sensor, 
which oscillates, is sampled at various temporal points and averaged to 
provide stabilized data for the residual quantity or density of the toner. 
The thus averaged toner residual quantity values are compared with a 
near-empty value or an empty value, and a toner near end signal or a toner 
end signal is correctly provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 6 is a schematic view showing an apparatus which embodies a toner 
detecting device in accordance with the present invention. The apparatus 
includes a developing unit 1, a photoconductor drum 2, a process motor 3 
for rotating a mixing member a process motor driving circuit 4, a 
rotational speed detector 5 for detecting the rotational speed of the 
process motor 3 and providing a constant speed signal CVE once the motor 
speed reaches a specific speed, an AD converter 6 for converting the 
output of a toner sensor 30, and a signal processor 7 for averaging output 
values of the toner sensor 30 and providing data for the residual quantity 
(or density) of the toner 9. 
Developing unit 1 has a mixing chamber 10 for mixing the toner 9 stored in 
toner container 12 with the mixing member 11 rotated by the process motor 
3. Unit 1 has a toner separating portion which includes a magnet roll 21 
for guiding the toner toward the photoconductor drum 2, and a doctor blade 
22 for regulating the thickness of the toner. Toner sensor 30 is included 
for detecting the residual quantity or density of the toner 9. The toner 9 
is, for example, a 1.5 component developer in this embodiment. 
The signal processor 7 comprises a microcomputer which includes an 
input/output (I/O) interface 71, a central processing unit (CPU) 72, a 
read only memory (ROM) for storing a program, and a random access memory 
(RAM) for storing various data. The I/O interface 71, the CPU 72, the ROM 
73, and the RAM 74 are interconnected by bus line 75. 
FIG. 7 is an explanatory diagram showing the contents of the RAM 74 of FIG. 
6. A variety of data, such as ADCR, TNSBUF, TNEMPC, STNR, STEND, and so 
on, which will be explained later, are stored and reviewed by new data in 
RAM 74. 
FIG. 8 is a diagram showing the relationship between the rotational speed 
of the mixing member 11 and the output voltage Vo of the toner sensor 30 
in detecting the residual quantity of the toner 9. When the mixing member 
11 is rotated at a constant speed, the output voltage Vo of the toner 
sensor 30 forms a regular waveform during a rotational period of the 
mixing member 11 due to a balance between the movement of the toner 9 and 
the responding speed of the toner sensor 30. When the output voltage Vo of 
the toner sensor 30 is sampled several times at fixed intervals and 
averaged to provide data for the residual quantity of the toner 9, sudden 
fluctuations in the output voltage Vo of the toner sensor 30 are absorbed 
to stabilize the data for the residual quantity of the toner 9. 
The period of the waveform of the output voltage Vo of the toner sensor 30 
agrees with the rotational period of the mixing member 11, so that the 
data for the residual quantity of the toner 9 may be more stabilized and 
may be more reliable if a period for averaging the sampled values is set 
to be substantially a random number times the rotational period of the 
mixing member 11. In FIG. 8, the term Vom represents the averaged value 
(data for the residual quantity of the toner 9) calculated with an 
averaging period of twice the rotational period of the mixing member 11, 
and the term Vom' represents an averaged value (data for the residual 
quantity of the toner 9) calculated with an averaging period of 2.5 times 
the rotational period of the mixing member 11. With the averaging period 
of twice the rotational period, the data for the residual quantity of the 
toner 9 is constant. On the other hand, with an averaging period of 2.5 
times the rotational period, the data for the residual quantity of the 
toner 9 pulsates. 
FIG. 9 is a flowchart showing one embodiment of the method cf detecting the 
residual quantity of the toner according to the present invention executed 
during each toner sampling period. The detecting period of the toner 
amount is 1.2 sec., which is a random number times the mixing period, 
i.e., one rotational time of the mixing member 11, and the number of 
samplings is 200 times per 1.2 sec. In this embodiment a new sampled value 
ADCR in the processor 7, which is equal to the output value A of the A/D 
converter 6, and a previous average TNSBUF are averaged as follows: 
EQU TNSBUF.rarw.(ADCR+TNSBUF)/2. 
The CPU 72 of the signal processing portion 7 monitors whether or not the 
rotational speed of the process motor 3 is constant, so that at step 901, 
it is determined whether or not the process motor speed is constant. When 
the rotational speed detecting portion 5 provides a constant speed signal 
CVE and when it a sampling time arrives, the CPU 72 checks to see whether 
or not an empty counter TNEMPC (initially 0) stored in the RAM 74 is 0, 
thereby it is determined whether or not the empty counter TNEMPC is equal 
to 0 at step 902. 
At first, the result of the determination at step 902 will be "YES" because 
the empty counter TNEMPC is set to 0 after the initialization, so that the 
control proceeds to step 903. An output A of the AD converter 6 is set in 
the RAM 74 as ADCR at step 903 and as TNSBUF at step 904. 
If the process is not in the initial stage, i.e., the empty counter is not 
0 at step 902, the control proceeds to step 905. At step 905, the output A 
of the AD converter 6 is read at a sampling time and set as ADCR, and the 
TNSBUF indicating the residual quantity of the toner is updated as 
follows: 
EQU ADCR.rarw.A 
EQU ADCR.rarw.ADCR+TNSBUF 
EQU TNSBUF.rarw.ADCR.div.2. 
At step 906, the empty counter TNEMPC is incremented by +1 (TNEMPC+1) and 
at step 907, it is determined whether or not the count value of the empty 
counter TNEMPC is more than or equal to 200, i.e., whether or not the 
sampled value averaging period of 1.2 sec. has passed. If the empty 
counter TNEMPC is less than 200, the control proceeds to step 916 and this 
routine is completed. Then the steps starting from step 901 are repeated 
after the sampling time and steps 901 to 907 are repeated until the 
counter TNEMPC counts 200. 
If the counter TNEMPC is more than or equal to 200 at step 907, the control 
proceeds to step 908 and it is determined whether or not the TNSBUF, which 
is indicating the threshold value of 3.25 V at step 908. If 
TNSBUF.gtoreq.3.25 V, the control proceeds to step 909, 912 and 913 
accordingly in which a near empty flag STNR (initially 0), a toner end 
flag STEND (initially 0), and the empty counter TNEMPC are cleared to 0. 
Then the control proceeds to step 916 to complete this routine, and the 
steps starting from step 901 are repeated. 
As the toner is consumed, the TNSBUF indicating the residual quantity of 
the toner may become smaller than the near empty threshold value of 3.25 
V. Then, if TNSBUF&lt;3.25 V at step 908, the control proceeds to step 911 in 
which the near empty flag STNR is set to 1, and a toner near the end 
detected signal is provided to display this situation on a display portion 
of the apparatus which will be explained later. 
At step 911, it is determined whether or not the TNSBUF is smaller than an 
empty threshold value of 2.90 V, and if TNSBUF.gtoreq.2.90 V, the control 
proceeds to step 912 and 913 and a toner end flag STEND (initially 0), and 
the empty counter TNEMPC are cleared to 0. 
If the toner is not replenished and is further consumed, and if the value 
TNSBUF indicating the residual quantity of the toner becomes smaller than 
the empty threshold value of 2.90 V, the indication of step 911 will be 
"YES." If TNSBUF &lt;2.90 V, the control proceeds to step 914 and the toner 
end flag STEND is then set to 1, and a toner end detected signal is 
provided to display this situation on the display portion of the 
apparatus, which will be explained later. 
Then at step 915, the empty counter TNEMPC is cleared to 0, and this 
routine is completed at step 916. 
When the residual quantity or density of the toner is first sampled after 
the mixing member 11 reaches a specific constant speed and turns at least 
one round, the toner which has gathered in clods will be separated into 
particles, and the toner which has stuck to the walls will be removed to 
provide more stabilized data for the residual quantity of the toner. 
FIG. 10 is a flowchart showing another embodiment of the method of 
detecting the residual quantity of the toner according to the present 
invention. In this embodiment, only the calculation of the value TNSBUF 
indicating the residual quantity of the toner is different from the 
embodiment shown in FIG. 9, so that the same steps as in FIG. 9 indicate 
the same step number. In the former embodiment, the residual quantity of 
the toner indicating value TNSBUF is calculated at every sampling time 
period, although it is calculated at every sampled value averaging period 
of 1.2 sec. 
Accordingly, in this embodiment, it is determined whether or not the empty 
counter TNEMPC is equal to the number of sampling times of 200 in 1.2 sec. 
at step 1001 after the execution of step 901. If TNEMPC.noteq.200, the 
control proceeds to steps 1002, 1003 and 1004. At step 1002, the output A 
of the AD converter 6 is read and set as AECR, and at step 1003, the 
TNSBUF indicating the residual quantity of the toner is accumulated by 
ADCR as follows: 
EQU TNSBUF.rarw.TNSBUF+ADCR. 
Then at step 1004, the empty counter TNEMPC is incremented by +1 (TNEMPC+1) 
and this routine is completed at step 916. 
On the other hand, if the empty counter TNEMPC is equal to the number of 
sampling times of 200 in 1.2 sec. at step 1001, the control proceeds to 
step 1005 in which the residual quantity of the toner indicating value 
TNSBUF, which is 200 accumulation of ADCR, is divided by 200 to calculate 
the average value of the output A of the AD converter 6. Explanation of 
steps 908 to 916 is omitted here since these step have already been 
explained in connection with FIG. 9. 
FIG. 11 is a flowchart showing one embodiment of an alarm operation when 
the amount of the toner is less than the predetermined value according to 
the present invention. At step 111, it is determined whether or not the 
near empty flag STNR is equal to I. If STNR.noteq.1 at step 1111, this 
routine is completed at step 116, but if STNR=1 at step the control 
proceeds to step 112 to determine whether or not the toner end flag STEND 
is equal to 1. 
If STEND.noteq.1 at step 112, the control proceeds to step 13 in which an 
alarm lamp is turned ON to indicate that the amount of toner is decreased. 
And if STEND=1 at step 112, the control proceeds to steps 114 and 115. At 
step 114, the printing operation of the image forming device is stopped 
and at step 115, the toner end lamp is turned ON to indicate the need for 
replenishment of the toner or the exchange of the toner container. 
The embodiment mentioned above detects the residual quantity of the toner. 
The sample arrangement is applicable for detecting the density of the 
toner. FIG. 12 is a schematic view showing an embodiment of the apparatus 
for detecting the density of the toner according to the present invention. 
In this embodiment, a toner replenishing container 8 which has a toner 
feed roller 81 at the bottom thereof is added on top of the toner 
container 12. The container 8 contains a quantity of the toner 9. 
FIG. 13 is a flowchart showing one embodiment of a toner supply operation 
of the image forming device shown in FIG. 12. At step 131, it is 
determined whether or not the near empty flag STNR is equal to 1. If 
STNR.noteq.1 at step 131, this routine is completed at step 135, but if 
STNR=1 at step 131, the control proceeds to step 132 to determine whether 
or not the toner end flag STEND is equal to 1. 
If STEND.noteq.1 at step 132, the control proceeds to step 133 in which the 
toner feed roller 81 is rotated 5 times to feed a small amount of toner 9 
to the toner container 12. And if STEND=1 at step 132, the control 
proceeds to step 134 in which the toner feed roller 81 is rotated 20 times 
to feed a large amount of the toner 9 to the toner container 12. 
The embodiment mentioned above observes whether or not the residual 
quantity of the toner has become smaller than the near empty threshold or 
the empty threshold, and if it is smaller than one of them, provides the 
toner near end signal or the toner end signal. Instead, the value TNSBUF 
indicating the residual quantity of the toner may be provided. 
Although the invention has been explained with reference to the 
embodiments, the invention allows various modifications without departing 
from the spirit of the invention described in the claims. These 
modifications are understood to be within the scope of the invention. 
As mentioned above, after the mixing member reaches a specific rotational 
speed and after the output voltage Vo of the toner sensor provides a 
regular waveform, the invention averages sampled values to provide data 
for the residual quantity or density of toner. This data for the residual 
quantity or density of the toner provided by the invention is stabilized 
because the data is not influenced by the rotation or stopping point of 
the mixing member. 
After the mixing member reaches a specific speed and turns at least one 
further rotation, the invention starts to sample the residual quantity or 
density of the toner, so that the clods of toner will have been separated 
into particles and the toner sticking to walls will have been removed, 
thereby providing more stabilized data for the residual quantity or 
density of the toner. 
The invention averages sampled values of the output voltage of the sensor 
for a period that is a random number times a rotational period of the 
mixing member, to provide data for the residual quantity or density of the 
toner. Namely, the output voltage of the toner sensor that fluctuates is 
sampled at various temporal points and averaged to provide stabilized data 
for the residual quantity or density of the toner. The averaged residual 
quantity of the toner is compared with a near empty value or an empty 
value to correctly provide a toner near end signal or a toner end signal.