GB1597753A

GB1597753A - Apparatus and methods of detecting a residual amount of magnetic developer in a nonmagnetic container

Info

Publication number: GB1597753A
Application number: GB823878A
Authority: GB
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1977-03-10
Filing date: 1978-03-02
Publication date: 1981-09-09
Also published as: DE2810502C2; DE2810502A1

Description

(54) IMPROVEMENTS IN AND RELATING TO APPARATUS AND METHODS OF DETECTING A RESIDUAL AMOUNT OF MAGNETIC DEVELOPER IN A NON-MAGNETIC CONTAINER (71) We, RICOH COMPANY, LTD., A Japanese Body Corporate of 34, l-chome Naka Magome, Ohta-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This present invention relates to apparatus and methods for detecting a residual amount of magnetic developer in a non-magnetic developer dispensing container.

According to the invention there is provided a method for detecting a residual amount of a magnetic developer in a nonmagnetic dispensing container comprising the steps of positioning the container in a predetermined position to dispense developer therefrom, arranging for at least one detection coil to lie adjacent the container when in the predetermined position to magnetically couple residual developer in the container, energising the coil to oscillate at a frequency dependent upon the amount of residual developer with which the detection coil couples, comparing the oscillation frequency with a predetermined reference frequency indicative of a predetermined residual developer in the container and providing an output indicative of the difference between the oscillation frequency and the predetermined reference frequency to indicate the amount of residual developer in the container.

According to the invention there is further provided apparatus for detecting a residual amount of a magnetic developer in a dispensing container made of nonmagnetic material comprising support means for supporting the container in a predetermined position, at least one detection coil mounted on the support means to lie adjacent the container when in said predetermined position and at a location so as to magnetically couple the residual developer in the container and an oscillation circuit incorporating said detection coil operable to oscillate at a frequency dependent upon the amount of developer with which said coil is coupled.

According to the invention, there is still further provided apparatus for detecting a residual amount of a magnetic developer in a dispensing container made of nonmagnetic material, means for supporting the container in a predetermined position, a detection coil mounted on the support means to lie in a location to magnetically couple residual developer in the container when the container lies in the predetermined position, means for energising the coil to cause the coil to oscillate at a frequency dependent upon the amount of residual developer with which the coil couples, a container detection switch for detecting the presence or absence of said container in said predetermined position, a detection circuit for determining the residual amount of developer in response to the oscillation frequency of the detection coil, and a discrimination circuit for detecting the presence of absence of the developing agent based on an output from said detection circuit and the output from said container detection switch.

Apparatus and methods embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a schematic view of a magnetic developing agent feed system in which the present invention is incorporated; Figure 2 is a diagram showing one example of the circuit of the apparatus for determining the residual amount of a magnetic developing agent; Figure 3 is a front perspective view of an apparatus which comprises a detection coil for determining the residual amount of a developing agent within a developing agent container; Fig. 4 is a side view of the apparatus shown in Fig. 3; Fig. 5 is a view similar to Fig. 4 but showing one embodiment of the apparatus according to the invention; Fig. 6 is a fragmentary view corresponding to Fig. 5 but showing another embodiment of the invention;; Fig. 7 is a view correspond to Fig. 6 but showing still another embodiment of the invention; Fig. 8 is a front sectional view of still another embodiment; Fig. 9 is a front sectional view of still another embodiment; Fig. 10 is a sectional view taken along the line X-X in Fig. 1; Fig. 11 is a sectional view showing a defect of an apparatus having no relevance to the invention; Fig. 12 is a schematic front view of still another embodiment; Fig. 13 is a sectional view of still another embodiment; Fig. 14 is a schematic front view of a further embodiment; Fig. 15 is a view in explanation of the relation between the container detection switch and a container; and Fig. 16 is a diagram showing one example of the circuit of the apparatus for effecting the detection of a container by the detection switch shown in Fig. 15 and the apparatus for detecting the presence or absence of a developing agent within the container.

The invention will now be described with reference to various embodiments thereof shown in the accompanying drawings. In Fig. 1, a developing agent container 1 made of a nonmagnetic material contains therein a magnetic developing agent 2 which is dispensed little by little by a developing agent dispensing mechanism 3 attached to an outlet port at the lower end of the container 1 and supplied to a developing station, not shown, of a copying apparatus.

Mounted adjacent the outer periphery of the lower portion of the outer periphery of the container I is a detection coil L which is adapted to determine the residual amount of the developing agent 2 within the container 1. The numeral 4 designates a port formed in the upper end of the container I and a lid therefor, the port being used for replenishing the container 1 with a developing agent when the developing agent in the container 1 is depleted.

The detection coil L, which is a resonance element of an oscillator, is connected, for example, to capacitors Cl and C2 as shown in Fig. 2 and constitutes a Colpitts oscillator 5 together with a transistor Q. The inductance of the detection coil L undergoes variations in accordance with the presence or absence of the magnetic carrier or magnetic toner of the developing agent 2 or the residual amount thereof, and the oscillation frequency of the oscillator 5 also undergoes variations accordingly. The oscillation frequency is low when the developing agent 2 Is present within the container 1, and becomes high as the amount of the developing agent 2 is reduced. The reason why a nonmagnetic material is used for constructing the container 1 is that if a magnetic material were used for this purpose the inductance would have little or no variations.It is desirable that the container 1 be made of an insulating material of nonmagnetic nature in order to reduce the loss of output of the oscillator 5.

The output of the oscillator 5 is transmitted, through a coupling capacitor C3, to a demodulator 6 which includes a phase-locked loop integrated circuit NE565A (a trade name of Signetics Corporation) functioning to convert, into a DC current, the difference between a frequency fl which is determined by a time constant of a variable resistor VRI and a capacitor C4 and a frequency f2 put in the integrated circuit through the coupling capacitor C3. The frequency fl is set at a level such that the output of the modulator 6 is brought to a low level when the developing agent 2 is present within the container 1 and brought to a high level when the developing agent is depleted, by the variable resistor VRI. However, if necessary, the frequency fl may be set at any other value as desired.

The output of the demodulator 6 is buffered by an amplifier 7 and transmitted to an integrator 8 which detects the output voltage of the amplifier 7 while removing noise caused to occur by the low fluidity of the developing agent 2, and produces a developing agent residual amount detection signal.

The described apparatus effects the determination of the residual amount of the magnetic developing agent on the basis of variations in oscillation frequency caused by changes in the inductance of the detection coil L. Therefore, the apparatus enables the determination to be effected accurately and positively without interfering with the flow of the developing agent. The use of a magnet arranged in the vicinity of a developing agent container would necessitate the use of means for agitating a magnetic developing agent because the magnetic developing agent is influenced by the magnetic attracting force of the magnet and held in one position. The apparatus dispenses with such agitating means.Also, since the oscillation frequency of the oscillator 5 shows subtle changes depending upon the presence or absence of the residualamount of the developing agent it is possible to determine the residual amount at any time as desired. Thus by positioning the detection coil L at any vertical level as desired relative to the container 1, it is possible to determine presence or absence of a given residual amount of the developing agent at any level as desired.

The container 1 may be supported by support means (not shown) in a tilting position as shown in Fig. 3 and rotated in the direction of an arrow so as to dispense the developing agent 2 through a dispensing port 9 formed at the lower end of the container 1. When this is the case, the developing agent 2 will be gradually moved downwardly by gravity as its amount is reduced. The developing agent thus moved downwardly and collected at the bottom of the container 1 is scooped up by a dispenser tube 10 which is rotatably supported. The developing agent scooped up by the dispenser tube 10 is agitated and mixed together by a swirling member 11 mounted within the tube 10 before being discharged through an outlet port of the tube 10.

Therefore, if the detection coil L which is a constituent of the oscillator 5 is arranged in juxtaposed relation to the outer periphery of the lowest portion of the container 1 in which the developing agent 1 gathers together, it is possible to determine the presence or absence of a residual amount of the developing agent 2 based on the oscillation frequency which undergoes a change as the inductance of the detection coil L varies in accordance with a change in the residual amount of the developing agent 2.

However, when the residual amount of the developing agent 2 becomes small, the developing agent 2 forms a mass which is disposed in a position a as shown in Fig. 4 in case the container 1 remains stationary, but the mass of developing agent 2 shows a phenomenon such that it moves slightly together with the container 1 to a position b due to frictional dragging and remains in position b as the container 1 rotates.

Therefore, if the detection coil L is disposed in juxtaposed relation to position a, a misoperation of the residual amount determining apparatus would occur in which the apparatus would give indication of the absence of the developing agent 2 while the dispensing device is operative and the container 1 is rotating, and would give indication of the presence of the residual amount when the container 1 stops rotating.

This problem can be solved by arranging the detection coil L in a position which is slightly displaced in the direction of rotation of the container 1 from the position in which the developing agent 2 gathers together when the container 1 is stationary.

In the event that the mass 2a of the developing agent 2 gathering together in position a when the container 1 is stationary and the mass 2b of the developing agent 2 gathering together in position b when the container 1 rotates partly overlap as shown in Fig. 5, it is possible to determine the presence or absence of a residual amount of the developing agent 2 substantially accurately regardless of whether the container 1 is stationary or rotating, if a detection coil L' is arranged such that it is juxtaposed against the overlapping portion of the masses 2a and 2b.

In the event that the mass 2a of the developing agent gathering together in position a when the container 1 is stationary is completely separated from the mass 2b of the developing agent 2 gathering together in postion b when the container 1 rotates, because of the velocity of rotation of the container 1 or the fluidity of the developing agent 2 as shown in Fig. 6, the desired effect can be achieved if a detection coil L" larger in size than the detection coil L' is used and arranged in a position slightly displaced from the mass 2a and substantially corresponding to the position of the detection coil L' shown in Fig. 5.

If it is not desirable to increase the size of the detection coil L", the detection coil L" may be divided into two detection coils L"a and L"b as shown in Fig. 7. The coil L"a will detect the residual amount of the developing agent 2 primarily when the container 1 is stationary and the coil L"b will detect the residual amount of the developing agent 2 primarily when the container 1 is rotating, and the resultant inductance of the two detection coils L"a and L"b will be determined. By this arrangement, it is possible to achieve the same effect as achieved when a single detection coil is used. Also, this arrangement makes it possible to accurately determine the presence or absence of a residual amount even when the residual amount in the container 1 has become very small.

In the container I shown in Fig. 3, a hollow space or cavity tends to be temporarily formed immediately after the dispenser tube 10 begins to rotate through the mass of developing agent 2 while scooping up a quantity of the developing agent 2, if the residual amount of the developing agent 2 becomes small.

Generally, the dispenser tube 10 is constructed such that it can scoop up the developing agent 2 from the lowest portion of the collected developing agent 2.

However, if the detection coil L is arranged in a position which is juxtaposed against the path of travel of the forward end of the scooping portion of the rotating dispenser tube 10, there is the danger of the residual amount being misjudged because the detection coil L will give indication of the absence of the developing agent 2 each time the dispenser tube 10 passes by the detection coil L in its rotary motion. Also, if the rotating dispenser tube 10 stops in a position in which it is juxtaposed against the detection coil L, then there is a possibility that the result of detection does not indicate the actual condition of the developing agent 2.

The aforementioned problem can be solved by arranging the detecting coil L in a position which is disposed out of the path of movement of the forward end of the scooping portion of the developing agent dispenser tube 10 or other dispensing device for the developing agent 2 as shown in Fig.

8. Since the detection coil L" is disposed in a position which is out of the path of movement of the forward end of the scooping portion of the developing agent dispenser tube 10, the coil L" is not affected by a cavity which would be temporarily created in the wake of the rotating dispenser tube 10 and can accurately determine the residual amount of the developing agent 2 within the container 1, no matter where the dispenser tube 10 may stop rotating.

Preferably, the detection coil L" is.

arranged in a position which is slightly displaced axially from the scooping portion of the dispenser tube 10, by taking into consideration the need to increase the efficiency with the developing agent 2 can be dispensed.

In the arrangement shown in Fig. 1 in which the container 1 is arranged an upright position and the developing agent 2 is dispensed through the bottom of the container 1 by means of the dispensing mechanism 1, the same effect as described above can be achieved by arranging the detection coil L in a position which is slightly above the dispensing mechanism 3.

In the case of a developing agent dispensing device of the interchangeable developing agent container type, there is the drawback of the dispensed developing agent dropping outside the developing tank in the developing station unless the replacing container is correctly set in the predetermined position, because the dispensing port of the replacing container is not indexed with the developing agent tank in this case.

In Fig. 9, an electrostatic latent image on a photosensitive member (not shown) is developed by the developing agent 2 in a developing agent tank 12. As the developing agent 2 which is consumed by a developing operation, the developing agent tank 12 receives a fresh supply of developing agent 2 from the developing agent container 1.

When the developing agent container 1 is mounted in placed in a tilting position as shown in Fig. 9, the dispenser tube 10 is mounted in the dispensing port in the lower portion of the container 1, and the container I and dispenser tube 10 are supported for rotation relative to each other.

As the dispenser tube 10 rotates, the developing agent disposed in the lowermost position of the container 1 is scooped by the scooping portion of the tube 10 and supplied through the dispensing port of the container I to the developing tank 12 while the developing agent is agitated and mixed well by the swirling member 11 while passing through the tube 10.

The detection coil L is arranged in a position in which the coil L is juxtaposed against the outer periphery of the lowermost portion of the container 1, and the residual amount of the developing agent 2 within the container 1 is detected on the basis of variations in the oscillation frequency of the oscillator which are caused by changes in the inductance of the coil L:'d L.

The detection coil L is fixed in place and adapted to be disposed in the predetermined position even if the old container 1 is replaced by a new container 1 by withdrawing the old container and inserting the new one in the directions of arrows.

If the developing agent within the container 1 is depleted, then the oscillation frequency of the oscillator 5 indicates that no developing agent is present within the container 1. Upon the empty container 1 being replaced by a new container 1 containing a predetermined quantity of developing agent therein, the presence of the developing agent is detected by the detection coil L and indication is given that there is a presence of developing agent within the container 1. If the replacing new container 1 is not set in the correct position, the coil L will be spaced from the outer periphery of the container 1 a distance which is greater than a predetermined distance.The existance of a greater distance than the predetermined distance between the coil L and the container 1 makes it impossible for the coil L to detect the amount of magnetism of the developing agent, and such situation is analogous to the situation in which there is no developing agent within the container 1. Thus indication is given that there is no developing agent. If it is possible to detect, either visually or by weighing the container, that the replacing container I contains a developing agent therein, the operator can detect the abnormality because the absence of the developing agent is indicated in spite of the. fact the developing agent is contained in the container. Stated differently, improper mounting of the replacing container 1 can be detected, so that the operator can mount the replacing container in the correct position.

Thus by positioning the detection coil L in such a manner that the residual amount can be determined in a normal way when the replacing container 1 is correctly mounted and the absence of the developing agent is indicated when the replacing container I is improperly positioned, it is possible not only to determine correctly the residual amount of the developing agent 2 but also to detect whether the replacing container is correctly positioned.

In the detecting apparatus, it is advantageous that the detection coil L be shaped such that it conforms to the shape of the outer periphery la of the container 1, in order that the magnetic flux produced by the coil L can satisfactorily penetrate the developing agent 2 within the container 1 and can increase the degree of a change in the oscillation frequency of the oscillator 5 which would be caused by the presence or absence of the developing agent 2. In case the container 1 is cylindrical in shape, the coil L will be circularly arcuate in shape as shown in Fig. 10 so as to conform to the outer periphery la.This brings the outer periphery 1 a into agreement with the magnetic flux generating surface of the coil L, so that the magnetic flux will penetrate the developing agent 2 within the container I and enable a changes in the oscillation frequency of the oscillator 5 to be detected accurately. In Fig. 11, there is shown a detection coil L of a shape which does not meet the aforementioned requirement. It will be understood that the magnetic flux is kept from satisfactorily penetrating the developing agent 2 within the container 1 in the case of the detection coil L of the shape shown in Fig. 11.

In case the container 1 is not cylindrical in shape, the coil L has only to be constructed such that its shape may conform to the shape of the outer periphery of the container 1. Also, the coil L may be shaped and arranged such that it conforms to the curved surface of the shoulder of the container 1 as shown in Fig. 12. If the coil L is of the type which has a core, the core may be shaped to conform to the shape of the outer periphery of the container 1 as shown in Fig. 13 which shows a core 15 of the E type having an outer end shaped to conform to the outer periphery la of the container 1.

As is well known, the core is made of a material of high magnetic permeability, and the use of a core has the effect of enchancing the magnetic force coupling the developing agent within the container 1.

Fig. 14 shows an example in which the coil L is wound on the container 1. The arrangement shown in Fig. 14 is advantageous because the magnetic flux positively passes through the developing agent in the container 1.

In order to ensure that the abnormal mounting of the container 1 is detected, a container detection switch SW shown in Fig. 15 may be used. The container detection switch SW is one which is actuated by a new container 1 mounted in the proper position when the old container 1 which has become empty is replaced by a new container 1 full of the developing agent or by the old container in which a fresh supply of the developing agent is filled. In the example shown in Fig. 15, the switch SW is a microswitch having a contact adapted to be turned on when an actuator of the microswitch is pressed by the shoulder of the container 1.

Fig. 16 shows one example of the circuit for detecting the presence or absence of the developing agent by using an embodiment of the invention provided with the container detection switch SW shown in Fig. 15. In Fig. 16, the numeral 18 designates a flip-flop functioning as a memory. In this embodiment, the flip-flop 18 is a multiple-input R--S flip-flop using a NAND gate 2. The flip-flop 18 has an S input terminal connected through an inverter 17 to a detector 16 for detecting the presence or absence of the developing agent, and a first R input terminal connected through a monostable multivibrator 19 to the container detection switch SW. The detector 16 for detecting the presence or absence of the developing agent includes, for example, the detection circuit shown in Fig. 2.

The switch SW is connected through a resistor R to a DC power source Vcc. The monostable multivibrator 19 of this embodiment includes the NAND gate 20, a delay circuit consisting of a resistor Rl inserted between one input terminal of the gate 20 and the switch SW and a capacitor Cl, and an inverter 21 inserted between the other input terminal of the NAND gate 20 and the switch SW. When the container 1 is mounted in the predetermined position as shown in Fig. 15, or when the switch SW is in its ON position, one input of the NAND gate 20 is at a high level and the other input thereof is at a low level, so that the output of the NAND gate 20 is at a high level. Thus so long as the container 1 is mounted in the predetermined position, the flip-flop 18 is not reset by the monostable multivibrator 19.

Assume that the developing agent 2 within the container 1 reaches a level at which an additional supply is required. Then the output of the integrator 8 of the detection circuit shown in Fig. 2, for example, is transmitted to the inverter 17 from the detector 16 for detecting the presence or absence of the developing agent, or a developing agent depletion detection signal of a high level is generated.

This signal is inverted by the inverter 17 and supplied to the S input terminal of the flipflop 18, thereby setting the flip-flop 18 produces a Q output of high level and actuates a lamp, buzzer or other indicator, not shown. The output signal of the flip-flop 18 may be used as a control signal for inhibiting copying. By virtue of the memory action of the flip-flop 18, the Q output terminal thereof is maintained at the high level even if the developing agent depletion signal subsegmently disappears or appears again.

If the empty container 1 is withdrawn from its normal position to fill it with a fresh supply of developing agent in accordance with an indication given by the indicator that the developing agent therein is depleted, then the switch SW is switched from its ON position to an OFF position. In the monostable multivibrator 19, the capacitor Cl is charged through the resistor Rl and one input terminal of the NAND gate 20 is brought to a high level. However, since the output of the inverter 21 is at a low level at this time, the output of the NAND gate 20 remains at a high level. That is, withdrawal of the empty container 1 does not result in resetting of the flip-flop 18.

If a new container 1 filled with the developing agent 2 or the old container 1 in which a fresh supply of developing agent is filled is mounted in the predetermined position as shown in Fig. 15, then the switch SW is turned on and the charge carried by the capacitor Cl is removed through the resistor R1 and switch SW. Stated differently, when the switch SW is closed, one input terminal of the NAND gate 20 is not brought immediately to a high level and remains at a low level for a certain period of time, and the other input terminal thereof is brought to a high level by the action of the inverter 21 as soon as the switch SW is closed.Because of this, the two inputs of the NAND gate 20 are temporarily brought to a high level, and a pulse of a low level is supplied as an output of the NAND gate 20 to the flip-flop 18 to reset the latter.

Thus the flip-flop 18 is automatically reset if the container 1 is mounted in its predetermined position after being filled with a fresh supply of developing agent, and the flip-flop 18 is restored to its initial position in which it is ready to detect the presence or absence of the developing agent 2 within the container 1.

A circuit consisting of a resistor R2, a diode D and a capacitor C2 and connected to a second reset input terminal R of the flip-flop 18 is a misoperation preventing circuit for bringing the flip-flop 18 to its initial position as a memory when the apparatus is connected to a power source.

This circuit may be dispensed with depending on the circumstances.

In the embodiments shown and described hereinabove, the container 1 has been described as being removed from its predetermined position and filled with a fresh supply of developing agent when it becomes empty or as being replaced by a new container full of the developing agent.

It is to be understood, however, that the container 1 can be used in any type of copying apparatus in which the container is moved in any way possible for filling it with a fresh supply of developing agent.

WHAT WE CLAIM IS: 1. A method for detecting a residual amount of a magnetic developer in a nonmagnetic dispensing container comprising the steps of positioning the container in a predetermined position to dispense developer therefrom, arranging for at least one detection coil to lie adjacent the container when in the predetermined position to magnetically couple residual developer in the container, energising the coil to oscillate at a frequency dependent upon the amount of residual developer with which the detection coil couples, comparing the oscillation frequency with a predetermined reference frequency indicative of a predetermined residual developer in the container and providing an output indicative of the difference between

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. agent includes, for example, the detection circuit shown in Fig. 2. The switch SW is connected through a resistor R to a DC power source Vcc. The monostable multivibrator 19 of this embodiment includes the NAND gate 20, a delay circuit consisting of a resistor Rl inserted between one input terminal of the gate 20 and the switch SW and a capacitor Cl, and an inverter 21 inserted between the other input terminal of the NAND gate 20 and the switch SW. When the container 1 is mounted in the predetermined position as shown in Fig. 15, or when the switch SW is in its ON position, one input of the NAND gate 20 is at a high level and the other input thereof is at a low level, so that the output of the NAND gate 20 is at a high level. Thus so long as the container 1 is mounted in the predetermined position, the flip-flop 18 is not reset by the monostable multivibrator 19. Assume that the developing agent 2 within the container 1 reaches a level at which an additional supply is required. Then the output of the integrator 8 of the detection circuit shown in Fig. 2, for example, is transmitted to the inverter 17 from the detector 16 for detecting the presence or absence of the developing agent, or a developing agent depletion detection signal of a high level is generated. This signal is inverted by the inverter 17 and supplied to the S input terminal of the flipflop 18, thereby setting the flip-flop 18 produces a Q output of high level and actuates a lamp, buzzer or other indicator, not shown. The output signal of the flip-flop 18 may be used as a control signal for inhibiting copying. By virtue of the memory action of the flip-flop 18, the Q output terminal thereof is maintained at the high level even if the developing agent depletion signal subsegmently disappears or appears again. If the empty container 1 is withdrawn from its normal position to fill it with a fresh supply of developing agent in accordance with an indication given by the indicator that the developing agent therein is depleted, then the switch SW is switched from its ON position to an OFF position. In the monostable multivibrator 19, the capacitor Cl is charged through the resistor Rl and one input terminal of the NAND gate 20 is brought to a high level. However, since the output of the inverter 21 is at a low level at this time, the output of the NAND gate 20 remains at a high level. That is, withdrawal of the empty container 1 does not result in resetting of the flip-flop 18. If a new container 1 filled with the developing agent 2 or the old container 1 in which a fresh supply of developing agent is filled is mounted in the predetermined position as shown in Fig. 15, then the switch SW is turned on and the charge carried by the capacitor Cl is removed through the resistor R1 and switch SW. Stated differently, when the switch SW is closed, one input terminal of the NAND gate 20 is not brought immediately to a high level and remains at a low level for a certain period of time, and the other input terminal thereof is brought to a high level by the action of the inverter 21 as soon as the switch SW is closed.Because of this, the two inputs of the NAND gate 20 are temporarily brought to a high level, and a pulse of a low level is supplied as an output of the NAND gate 20 to the flip-flop 18 to reset the latter. Thus the flip-flop 18 is automatically reset if the container 1 is mounted in its predetermined position after being filled with a fresh supply of developing agent, and the flip-flop 18 is restored to its initial position in which it is ready to detect the presence or absence of the developing agent 2 within the container 1. A circuit consisting of a resistor R2, a diode D and a capacitor C2 and connected to a second reset input terminal R of the flip-flop 18 is a misoperation preventing circuit for bringing the flip-flop 18 to its initial position as a memory when the apparatus is connected to a power source. This circuit may be dispensed with depending on the circumstances. In the embodiments shown and described hereinabove, the container 1 has been described as being removed from its predetermined position and filled with a fresh supply of developing agent when it becomes empty or as being replaced by a new container full of the developing agent. It is to be understood, however, that the container 1 can be used in any type of copying apparatus in which the container is moved in any way possible for filling it with a fresh supply of developing agent. WHAT WE CLAIM IS:

1. A method for detecting a residual amount of a magnetic developer in a nonmagnetic dispensing container comprising the steps of positioning the container in a predetermined position to dispense developer therefrom, arranging for at least one detection coil to lie adjacent the container when in the predetermined position to magnetically couple residual developer in the container, energising the coil to oscillate at a frequency dependent upon the amount of residual developer with which the detection coil couples, comparing the oscillation frequency with a predetermined reference frequency indicative of a predetermined residual developer in the container and providing an output indicative of the difference between

the oscillation frequency and the predetermined reference frequency to indicate the amount of residual developer in the container.

2. Apparatus for detecting a residual amount of a magnetic developer in a dispensing container made of non-magnetic material comprising support means for supporting the container in a predetermined position, at least one detection coil mounted on the support means to lie adjacent the container when in said predetermined position and at a location so- as to magnetically couple the residual developer in the container and an oscillation circuit incorporating said detection coil operable to oscillate at a frequency dependent upon the amount of developer with which said coil is coupled.

3. Apparatus according to claim 2, wherein the support means is arranged to support the container with the longitudinal axis of the container inclined to the vertical and to rotate the container about its longitudinal axis and wherein the detection coil is arranged on the support means to lie adjacent the lowermost portion of the container when supported by the support means.

4. Apparatus according to claim 2, wherein the support means is arranged to support the container with its longitudinal axis inclined to the vertical and to rotate the container about its longitudinal axis and wherein the detection coil is mounted on the support means to lie at a position intermediate the position in which residual developer accumulates when the container is stationary and the position in which residual developer accumulates when the container is rotated by the support means at a predetermined speed.

5. Apparatus according to claim 2, wherein the support means is arranged to support the container with its longitudinal axis inclined to the vertical and to rotate the container about its longitudinal axis, and wherein the detection coil is a single coil of a size such and so positioned that the coil extends over an area such that it encompasses both the area of the container around which residual developer accumulates when the container is stationary and the area of the container around which residual developer accumulates when the container is rotated by the support means at a predetermined speed.

6. Apparatus according to claim 2, wherein the support means is arranged to support the container with its longitudinal axis inclined to the vertical and to rotate the container about its longitudinal axis and wherein the detection coil includes two coil elements one element being supported in such a position that it will lie adjacent an area of the container where developer accumulates when the container is stationary and the other element is supported in such a position that it will lie adjacent an area of the container where developer accumulates when the container is rotated.

7. Apparatus according to any one of claims 3 to 6, wherein the detection coil is so orientated that unless the container is positioned on the support means within a predetermined range of said predetermined position there will be substantially no magnetic coupling of the coil with developer in the container.

8. Apparatus according to claim 2, wherein the support means is arranged to support the container with its longitudinal axis inclined to the vertical, and including a dispenser tube rotatably mounted on the support means to extend into the mouth of the container, the free end of the tube carrying a radially extending scoop to scoop developer from the container into the tube, and wherein the detection coil is located in a position in which it is longitudinally spaced from the locus of the scoop.

9. Apparatus according to any one of claims 2 to 8, wherein the detection coil is shaped to conform to the outer periphery of the container when in said predetermined position.

10. Apparatus according to any one of claims 2 to 8, wherein the detection coil has a magnetisable core which is shaped to conform to the outer periphery of the container when in said predetermined position.

11. Apparatus according to claim 2, wherein the container has a neck portion wherein the detection coil is wound so that it extends around the neck portion when the container is in said predetermined position.

12. Apparatus according to any one of claims 2 to 11, including a demodulator connected to demodulate the output of the oscillation circuit, an amplifier connected to amplify the output of the demodulator, and an integrator connected to integrate the output of the amplifier.

13. Apparatus for detecting a residual amount of a magnetic developer in a dispensing container made of non-magnetic material the apparatus comprising support means for supporting the container in a predetermined position, a detection coil mounted on the support means to lie in a location to magnetically couple residual developer in the container when the container lies in the predetermined position, means for energising the coil to cause the coil to oscillate at a freqency dependent upon the amount of residual developer with which the coil couples, a container detection switch for detecting the presence or absence of said container in said predetermined position, a detection circuit for determining the residual amount of developer in response to the oscillation frequency of the detection coil, and a discrimination circuit for detecting the presence or absence of the developing agent based on an output from said detection circuit and the output from said container detection switch.

14. Apparatus as claimed in claim 13, wherein said detection circuit comprises an oscillator which includes the detection coil as a resonant element, a demodulator connected to said oscillator, an amplifier connected to said demodulator, and an integrator connected to said amplifier.

15. Apparatus according to claim 13 or to claim 14, wherein the discrimination circuit comprises a memory arranged to be set by a developing agent depletion detecting signal from said detection circuit to produce an output signal, the memory being connected to said container detection switch in such a manner that said memory is reset by a signal indicating that the container is located in the predetermined position.

16. A method of determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described.

17. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

18. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

19. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

20. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

21. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

22. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.

23. Apparatus for determing a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

24. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 9 of the accompanying drawings.

25. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 10 of the accompanying drawings.

26. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 11 of the accompanying drawings.

27. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 12 of the accompanying drawings.

28. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 13 of the accompanying drawings.

29. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figure 14 of the accompanying drawings.

30. Apparatus for determining a residual amount of magnetic developer in a nonmagnetic dispensing container substantially as hereinbefore described with reference to Figures 15 and 16 of the accompanying drawings.

31. An electrophotographic copying machine including apparatus according to any one of claims 2 to 15 and 17 to 30.