GB2268807A - Detection of material consumption - Google Patents

Abstract

An arrangement for detecting the presence of a fluent material in a container (4) comprises a movable member (6) disposed within the container, excitation means (10), disposed outside the container (4), for applying a force to the movable member (6), and detection means (10), disposed outside the container (4), for detecting motion of the movable member (6) resulting from the applied force and for thereby detecting whether the material is present in the vicinity of the movable member (6). In the preferred embodiments, the movable member (6) comprises a magnetic member mounted on a spring and the excitation and detection means include a Helmholtz coil (10) for applying the magnetic force and providing a signal corresponding to the motion, respectively. The arrangement is suited, especially where disposable containers are used, to detecting the presence of toner powder or of fuser oil in a container in photocopying machines, or of ink in a cartridge in a printing device. <IMAGE>

Description

DETECTION OF MATERIAL CONSUMPTION The present invention relates generally to the detection of the presence of a fluent material, and more particularly to the detection of the consumption of toner powder or liquid ink from a container in a copying or printing device.

In conventional photocopiers the toner powder used in the xerographic process is consumed at varying rates. When all of the toner in a toner hopper has been consumed by a machine, in the case of a re-usable hopper the hopper is refilled from a supply of toner; in the case of a disposable hopper the existing hopper is removed and discarded and a full toner hopper fitted in the machine. Similarly, fuser oil cartridges in photocopiers and ink cartridges in printers often require refiliing or replacement during the lifetime of the machine. In all cases, it is highly undesirable for a lack of toner, ink, etc. to become apparent (e.g. as inadequate copy density) only when a consequent deterioration in the copying or printing quality of the machine is produced.

It is known to detect the complete consumption of toner from a toner hopper in photocopiers (an "out-of-toner" condition) using inter alia two techniques. According to the first of these, the inabilty of the machine to maintain adequate copy density, as measured by the automatic density control (ADC) system, is detected, and this condition is assumed to be due to the machine being out of toner. Often secondary measures are taken before out-oftoner is actually indicated, e.g. performing tone-ups to see if the copy density can be restored.

This process is used in many photocopier machines (for example, the XEROX 1045 family and the XEROX 5046 family). However, this technique can suffer from false out-of-toner indications, e.g. through toner bridging in the hopper. Also, if the ADC system fails, the ability to detect out-of-toner is lost.

According to the second technique, a piezoelectric crystal sensor is fitted in a toner hopper and the ability of the crystal to oscillate is monitored. The presence of toner on the crystal prevents it oscillating effectively, and thus the presence of toner is detected. This technique also finds widespread use in a number of photocopier machines. However, this method requires that electrical connections be made to the hopper assembly, which makes it unsuitable for user-replacable hoppers, in addition to the extra cost involved in throwing away a sensor every time a hopper is changed. It also suffers from false out-of-toner indications due to local cavitiation of toner in the vicinity of the sensor, and also from failure to detect out-oftoner when toner stays on the surface of the sensor even when the actual toner level falls.The piezoelectric crystal is very small and can actually cause cavitiation around itself when it oscillates. It is also very delicate and can easily be damaged.

There is therefore a need for an arrangement which overcomes these problems by having no electrical connections to the hopper and which interacts with a significant volume of toner in the hopper so as to eliminate false out-of-toner indications due to local cavitation.

There is also a need for an arrangement which has a sensor element inexpensive enough to throw away in a disposable hopper.

The present invention provides an arrangement for detecting presence of a fluent material, comprising: a container for the material; a movable member disposed within said container; excitation means, disposed outside said container, for applying a force to said movable member; and detection means, disposed outside said container, for detecting motion of said movable member resulting from the application of said force, and for thereby determining whether said material is present in the vicinity of said movable member. An advantage of the invention is that no electrical contact need to be made to the container. A further advantage of the invention is that most of the components of the arrangement are contained inside the machine in which the container is housed.A further advantage of the invention is that since there is a minimal component count within the container, the arrangement is highly suited to disposable containers. A further advantage of the invention is that the level of user maintenance required is minimised.

Preferably, said container is formed of a non-magnetic material; said movable member comprises a magnetic member; and said excitation means comprises electromagnetic excitation means, disposed outside said container, for applying a magnetic force to said magnetic member. Preferably, said electromagnetic excitation means includes a coil mounted outside said container; and said detection means is adapted to be coupled to said coil for detecting signals generated in the coil due to said motion of said magnetic member relative to a first position. Preferably, said excitation means includes means for applying a magnetic force to said magnetic member for a pre-determined period.An advantage is therefore that initiation of the magnetic member's displacement is externally controlled, so that detection of resulting signals is synchronised with the application of the magnetic force, thereby eliminating the need for constant monitoring and possible detection of false signals.

Alternatively, the force may be applied mechanically by means of the components, communicating with the interior of the container, which dispense the material from the container. Where the dispensing system includes a shaft-mounted auger flight, the shaft may be provided with one or more projections or spokes, whereby as the shaft rotates, at one or more points in the rotation of the shaft, the movable member is mechanically displaced and then freed. In this case, there is no need for the additional components (voltage source and switches) required to produce the electromagnetic excitation. At the same time, however, the time at which the displacement of the movable member occurs cannot be determined (without additional components) so that the detection coil has to be monitored continuously for the presence of signals.

Preferably, said movable member is provided on a resilient member within said container, said movable member having a first position corresponding to the equilibrium position of said resilient member. Preferably, said resilient member comprises an elongate strip of flexible material, one end of the strip being fixedly attached to a sidewall of the container, the opposite, free end being attached to said movable member. Preferably, said first position is adjacent one or more walls of said container, and, in the absence of said material from the vicinity of said movable member, said movable member is susceptible of substantially free movement. An advantage is therefore that the fundamental frequency of the movable member and resilient member is low (and sub-sonic) thus allowing high amplitude and long persistance in the displacement of the movable member and in the generated signals.A further advantage is therefore that the high vibration amplitude minimises false responses of the detection means due to local cavitation in the material bulk, which could occur with low amplitude systems.

Alternatively, the arrangement may be as described above with the exception that the resilient member is replaced by (1) one or more filaments, such as wire, (2) a pivoted andlor sprung lever, or (3) any similar arrangement whereby the movable member oscillates freely after displacement by said force.

Preferably, said container is substantially box-shaped and, in use, may be positioned with its sides vertical such that said resilient member extends from adjacent the top of the container and such that said movable member is disposed adjacent the base of said container.

Alternatively, the movable member may be disposed within the container with the resilient member extending horizontally, such that the movable member is capable of movement in a horizontal or vertical plane. Alternatively, the resilient member may be disposed in any other orientation convenient for a particular application.

Preferably, said force causes a maximum displacement of said movable member to a second position in the absence of said material from the vicinity of said movable member, said first and second positions defining a first direction, and the axis of said coil is substantially parallel to or aligned with said first direction. An advantage is therefore that the mechanical impulse applied to the movable member dislodges any fluent material that may adhere to the movable member as the container empties, thus ensuring reliable operation.

Preferably, said magnetic member comprises a permanent magnet or a material of high magnetic permeability, such as iron, silicon-iron, permalloy, supermalloy, my metal or ferrite.

Preferably, said detection means is enabled for a period corresponding to the decay time constant of the movable member and the resilient member from the second position to said first position.

Preferably, said detection means includes a delay circuit for setting the duration of said pre-determined period. An advantage of this feature is that since the time at which the movable member was displaced is known, the coil need be monitored for output signals only for a short time after the application of the force, thereby limiting the detection of false signals.

Preferably, said excitation means includes means for applying a time-varying force with frequency f to said magnetic member, where f is the fundamental frequency of said movable member and said resilient member. By repeatedly exciting the movable member at a repetition frequency f, for several cycles, this mass/spring assembly is caused to resonate, thus giving rise to a large amplitude of oscillation. In addition the direction of the current may be reversed every half cycle, further enhancing the effect.

Preferably, said detection means includes a switch, said coil being connected to an amplifier when said switch is in its NC position, and to a voltage supply when said relay switch is in its NO position. Preferably, said switch comprises a relay or one half of a DPDT relay.

Preferably, said detection means includes a demodulator circuit, coupled to the output of said amplifier, for generating a demodulated signal. Preferably, said demodulator circuit includes a diode-resistor-capacitor circuit.

The detection means may include a threshold detector, coupled to the output of said demodulator circuit, for comparing said demodulated signal with a pre-determined threshold.

The detection means may include a flip-flop, coupled to the output of said threshold detector and to a first monostable, the monostable being activated by the termination of said predetermined period to supply an enabling pulse to said flip-flop; wherein the output of said flip-flop activates an indicating means if said demodulated signal exceeds said pre-determined threshold during the duration of said enabling pulse. Preferably, said indicating means comprises an alphanumeric visual display, a LED or an audible indicator.

The detection means may include one or more cascaded further monostables constituting said delay circuit and coupled to said first monostable; wherein said predetermined period is initiated by the termination of said enabling pulse.

The detection means may include an input-output (I/O) port for coupling signals generated by said detection means to a software-controlled microcontroller or microprocessor.

The arrangement may include a plurality of movable members and a plurality of coils, the movable members being spaced from eachother at pre-determined intervals, and each coil being positioned adjacent a respective movable member; the arrangement thereby being adapted to determine partial and/or total consumption of said material from said container.

The container may comprise a user-replacable or permanently housed container in a xerographic or printing machine. The container may comprise a toner hopper, an ink cartridge, or a fuser oil cartridge. The fluent material may comprise a toner powder or any other particulate material, ink, oil or any other liquid. Alternatively, the fluent material may comprise a mixture of toner particles and magnetic carrier particles in any required weight ratio. In the case of developer material (comprising almost entirely magnetic carrier particles) the duration of the excitation force may be extended to ensure efficient detection.

Preferably, the arrangement further includes dispensing means, communicating with the interior of said container, for dispensing said material from said container at a predetermined rate. Preferably, said dispensing means includes a rotatable auger flight passing through a wall at the base of the container.

Preferably, the or each coil comprises a multi-turn Helmholtz coil. The or each coil may be provided with a ferrite and/or laminated high permeability core. An advantage of this feature is that it greatly increases the external magnetic field generated by the or each coil, permitting the use of a smaller magnetic member. A pair of Helmholtz coils may be used, one on each side of the container, thereby increasing the external magnetic field generated and thus the displacement of the magnetic member.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a simplified lateral view of an arrangement according to the present invention; Figure 2 illustrates the electromagnetic excitation and detection circuits according to a first embodiment of the present invention; Figure 3 shows the electromagnetic excitation and detection circuits according to a second embodiment of the present invention; Figure 4 illustrates a cross-sectional view of a toner hopper in an embodiment of the present invention; Figure 5 shows the electromagnetic excitation and detection circuits according to a third embodiment of the present invention; Figures 6 illustrates a timing diagram of the circuit of Fig. 5 when the toner hopper is full; and Figures 7 illustrates a timing diagram of the circuit of Fig. 5 when the toner hopper is empty.

Referring to Fig.1, a spring 2 in the form of a slender strip of plastic material is firmly embedded in an anchor 3 in the body of a plastics toner hopper 4 (only part of which is shown), while a magnet 6 is attached to the free end of the spring 2 by means of adhesive. With the toner hopper 4 empty spring 2 assumes the equilibrium position illustrated and the magnet 6 is positioned adjacent the wall 8 of the toner hopper 4; the magnet 6 is then susceptible to displacement substantially along the direction of arrow A. A multi-turn Helmholtz coil 10 is positioned outside the toner hopper 4 and adjacent the wall 8 such that its axis is generally aligned with the direction of arrow A. The ends 12 of coil 10 connect to excitation and detection circuits (not shown) which are described in detail below.

Turning to Fig.2, this illustrates the electromagnetic excitation and detection circuits according to a first embodiment of the present invention. In this embodiment the coil 10 is connected to a first relay switch 14 and a second relay switch 16, the relays 14, 16 having normally closed (NC) and normally open (NO) contacts as shown. The NO contact of relay 14 is connected to a low impedance voltage source 30. A capacitor 18, connected in parallel with the coil 10, absorbs high frequency noise signals occuring in the coil 10 but leaves low frequency signals unaltered. With the relays 14, 16 in the NC condition as shown signals from the coil 10 are fed to a high input impedance op-amp 20, via resistor 22, for amplification and subsequent detection by detection stage 28.A diode 23 across coil 10 dissipates the back EMF generated by coil 10 after a current pulse (discussed further below) applied to coil 10 terminates. Capacitors 24 and 26 are optional and are included if necessary for stabilising the circuit. Relay 14 is used to switch the coil 10 between a magnetic field generation mode (in which a current pulse is applied to the coil 10) and a magnetic field detection mode, which are described further below.

Relay 16 is used to short the non-inverting input of the op-amp 20 to ground while the current pulse is applied to the coil 10, and for some time afterwards until any back EMF in the coil 10 (discussed below) is dissipated, to prevent overload and blocking of the op-amp 20. The output of the detector 28 is passed, via an input-output (I/O) port (not shown) to a software-controlled microprocessor or microcontroller (not shown) of the copying machine in which the toner hopper is housed.

The theory underlying the operation of the arrangement is as follows. During each period that relays 14, 16 are in the NO condition, a current pulse is applied to the coil 10, causing a transient magnetic field to be generated by the coil 10. The interaction of the magnetic fields due to magnet 6 and coil 10 causes an impulse force to be applied to the magnet 6. In the absence of material (toner powder) from the vicinity of magnet 6 the latter is displaced by this force from the static equilibrium position shown in Fig. 1. Upon termination of the current pulse, the magnetic field generated by coil 10 collapses so that the magnetic force acting on magnet 6 becomes zero; the magnet 6, now displaced from its equilibrium position, starts to move back to that position under the restoring force of the spring 2. The ensuing motion of magnet 6 is one of damped mechanical oscillation about its equilibrium position at a frequency f, where f is the fundamental frequency of the magnet-spring combination. This motion causes a varying magnetic field of fundamental frequency f to appear in the plane of the coil 10, thereby inducing in the coil 10 a varying EMF, also of fundamental frequency f, by electromagnetic induction. The EMF thus generated is amplified and fed to a detector circuit which includes a Schmitt trigger for comparing the induced EMF with a reference voltage. In order to improve detection, the detector may optionally include a bandpass filter (not shown) with a pass band corresponding to the fundamental frequency f of the magnet/spring combination, so as to increase its signal-to noise ratio and eliminate false signals.

If, when the current pulse is applied, the magnet 6 is submerged in toner it experiences resistance to motion due to the presence of the toner: the initial displacement of the magnet is therefore very small, and subsequent oscillation is heavily damped and very short-lived. This is in contrast to the effect when the hopper is empty, whereby the oscillations are large and persist for a significant period after the end of the current pulse.

The sequence of operation of the arrangement is as follows. In the quiescent state (Fig. 2) the contacts of the relays 14, 16 are in the NC position so that the coil 10 is connected to the op-amp 20 which has its non-inverting input unclamped. At regular intervals (about every 100 seconds; see Figs 6 and 7) the following events occur. (1) Relay 16 is activated, causing its contacts to close and thus clamp the non-inverting input of the op-amp 20. (2) After a short delay, relays 14 is activated, thus connecting the coil 10 to the voltage source 30 so that a current flows in the coil 10. (3) After a further short period (about 100 ms; see Figs 6 and 7) relay 14 is deactivated, thereby terminating the current flow in the coil 10 and connecting the latter to the non-inverting input of the op-amp 20. (4) After a further delay of up to 100 ms, relay 16 is deactivated, thus unclamping op-amp 20 and allowing any EMF induced in the coil 10 to be passed to the op-amp 20, amplified and detected by the detector 28.

Should the detector 28 detect a persistent oscillating EMF, it follows that the toner hopper is empty, and on receiving this information the microcontroller (not shown) will cause an out-of-toner condition to be indicated. Otherwise, it follows that the toner hopper contains sufficient toner, and no such condition is indicated. The above sequence is repeated.

Referring to Fig. 3, this shows the electromagnetic excitation and detection circuits according to a second embodiment of the present invention. The principal and operation is the same as in the first embodiment, with the exceptions discussed below, and like reference numerals in Figs 2 and 3 denote like components.

In this second embodiment, magnet 6 is replaced by a piece 6 of magnetic material of high permeability, such as iron, silicon-iron, permalloy, supermalloy, mumetal or ferrite. In operation, upon application of the current pulse to the coil 10, a transient magnetic field is generated by the coil 10, as before. This causes a magnetic moment m to be induced in the piece 6 by magnetic induction.The interaction of the fields due to piece 6 and coil 10 causes an impulse force to be applied to the piece 6, dispiacing it lin the absence of toner in the vicinity from its static eqilibrium position; and upon termination of the curent pulse the piece 6 vibrates as described before in relation to the magnet 6.At the same time, the magnetic moment m collapses, except for the residual magnetisation due to magnetic (B-H) hysteresis, so that very little EMF is generated in the coil 10 as a result of the motion of the piece 6. However, the motion of the piece 6 causes the inductance L of the coil 10 to vary periodically with frequency f. This is detected by making coil 10 part of a tuned circuit of an a oscillator 32, which replaces the amplifier of the first embodiment, oscillating at a fundamental frequency F (F S f).

The variation of the inductance L of coil 10 due to the motion of the piece 6 causes the frequency of the oscillator 32 to vary periodically with frequency f, thus producing a frequencymodulated signal at the output of the oscillator 32. This signal is fed to detector 34 which, in this embodiment, includes a frequency-demodulator which removes the carrier frequency F; the original signal of frequency f is thereby retrieved, and processed as before.

Figure 4 illustrates a cross-sectional view of a toner hopper in one or more embodiments of the present invention. In a Xerox 5046 photocopier the toner hopper 4 is housed in the orientation shown, with its sidewalls 8 generally vertical. The spring 2 is anchored at anchor point 3 to the top 9 of the toner hopper 4, so that the spring 2 extends generally vertically. A shaft 7 carrying an auger flight (not shown) for dispensing toner from the toner hopper 4 extends into the paper in Fig. 4. The spring 2 is shown in its static equilibrium position, with the magnet or magnetic piece 6 adjacent both the shaft 7 and the sidewall 8 of the toner hopper 4.

A third embodiment of the present invention will be described with reference to Figs 5, 6 and 7. Referring to Fig. 5, this shows the electromagnetic excitation and detection circuits according to the third embodiment. The principal and operation is the same as in the first and second embodiments, with the exceptions discussed below, and like reference numerals in Figs 2,3 and 5 denote like components. [Figures 6 and 7 illustrates a timing diagrams of the circuit of Fig. 5 when the toner hopper is full and empty, respectively; Figs 6(a) to (h) and 7(a) to (h) represent the signals at points a to h in Fig. 5.] In the circuit of Fig. 5, timing is achieved by the use of three monostables 52, 54, 56 arranged in a ring. The output of the first monostable 52 is a series of pulses T1 (100 ms long) at intervals of about 100 s.Pulse T1 is simultaneously applied to the relays 14, 16 switching them from their NC contacts to their NO contacts for the duration of T1, thereby applying a current pulse (Figs 6(b), 7(b)) from voltage source 30 to the coil 10, and clamping the non-inverting input of op-amp 20, for that period. At the end of T1 second monostable 54, which determines the delay time, is triggered (Figs 6(f), 7(f)). During the delay pulse (T2) produced by the second monostable 54 the EMF induced in the coil 10 is amplified by the amplifier 20 and rectified by detector circuit 62 comprising D1, R1, C1.

With the hopper empty, the voltage across C1 is thus a d.c. voltage decaying with a time constant of s (see Fig. 6(d)). This voltage is fed to the input of a Schmitt trigger circuit 64, in which the threshold (trigger level) is set using conventional techniques, the output being HIGH or LOW (Figs 6(e), 7(e)) depending on whether the voltage across C1 is above or below the threshold. The output of Schmitt trigger circuit 64 is fed to the D input of D-type bistable 66. Upon termination of delay pulse T2 a trigger pulse is applied to the clock input (CLK) of the D-type 66; on receipt of this clock pulse the Q output of the D-type 66 assumes the state of the D input.Thus if there is no toner in the vicinity of the magnet 6, the Schmitt trigger output persists in a HIGH state (T3 in Fig. 6(e)), so on termination of T2, output Q,goes HIGH (see Figs 6(g)), switching ON transistor 68 and illuminating the out-of toner indicator (LED 70).

If there is sufficient toner in the hopper 4, no significant EMF is induced in the coil 10 (Fig. 7(d)), the D input is LOW on termination of the delay pulse T2 (Fig. 7(e) to (g)), so the out of-toner indicator is cancelled or remains off, as the case may be.

Whatever the condition of the circuit, it persists until the next clock pulse arrives at the D-type 66: the interval corresponds to the duration of delay pulse T4 (Figs 6(h), 7(h)) set by the third monostable 56, so that the above-described cycle is repeated. In general the out-oftoner indicator remains OFF while the toner level in hopper 4 is above the magnet-spring assembly and stays ON permanently when the hopper 4 is empty. There may however be a minor transition period where the state of the detection circuit fluctuates due to redistribution of toner within the hopper 4.

In the case where the software capability of the machine microcontroller is used in the foregoing embodiments, the functions of the excitation and/or detection circuits are implemented in part using software driven digital I/O, based on a CORA65 microcontroller. This allows synchronisation of the out-of-toner detection system to the rest of the machine and processing of the data to make better use of the signals. For example, the out-of-toner indication may be suppressed until the total dispense time following the initial detection of out-of-toner exceeds a preset period. Alternatively, the output (Figs 6(d), 7(d)) may be fed to an A/D converter and thus measured directly by the micro controller: the time profile of the detected signal may then be measured so that true signals are distinguished from false ones.

For example, in the embodiment of Figs 5 to 7, although all of the components of the circuit of Fig. 5 are illustrated as hardware elements, the functions of monostables 52, 54, 56 may be implemented using software-controlled timers and digital output ports (not shown); and the D-type 66 may be implemented using a digital input port (not shown) which is read when monostables 54 times out (T2 terminates), thus exactly simulating the operation of a hardware D-type flip-flop. In addition, transistor 68 and LED 70 may be replaced by the microcontroller-driven alphanumeric display (not shown) of the machine.

EXAMPLE 1 The invention has been implemented using the Xerox&commat; 5046 photocopier toner hopper shown in Fig. 4. The spring 2 comprised a strip, having dimensions 1x12x95 mm, cut from a sheet of plastic material. The magnet 6 comprised a household rubber magnet of the type used on refrigerator doors, and having dimensions 12x3.2 mm and a weight of 1.7 g. The coil 10 consisted of approx. 1100 turns of enamelled copper pile wire wound on a square former of 28 mm side and 16 mm in depth. The d.c. resistance of the coil was 45 n. The coil 10 was used in conjunction with "E" type laminations. The coil 10 was energised by applying a 50 ms pulse of 30 V to the coil, resulting in a steady state current of 0.67 A.After termination of the current pulse, with the hopper empty the EMF induced in the coil was -115 mV peak-to-peak a.c. at a frequency of -14 Hz, with a decay time constant of -3 s. On the other hand, with the magnet submerged in toner only a transient signal (see Fig. 7(d)) lasting less than 100 ms was obtained, most of which was due to the back EMF of the coil 10.

EXAMPLE 2 Example 1 was repeated using instead of toner a mixture of toner and magnetic carrier particles in a ratio of 3:1 by weight of toner to carrier (known as "replenisher") and found that the sytem operated successfully with no modification .

EXAMPLE 3 Example 1 was repeated using pure developer (comprising 98% magnetic carrier and 2% toner) as the material instead of toner and, with an adjustment of the signal timings, the sytem again operated successfully, indicating that the material is not limited to use only with non-magnetic powders.

When pure developer is used, the magnet at the end of the leaf-spring accumulates carrier beads and forms a magnetic brush in the form of a spiky sphere. This increases the mass at the end of the spring when it is removed from the powder, thus lowering the natural vibrational frequency. The vibrations however still persist for several seconds so can still be detected and easily differentiated from the case when the magnet is still immersed in the powder. A secondary effect that occurs is that the magnetic brush shunts some of the magnetic field lowering the external field. However this does not significantly seem to affect either the ability of the coil to deflect the magnet or to induce sufficient EMF in the coil afterwards to be easily detectable.

Due to the reduction in vibrational frequency mentioned above, the length of the excitation pulse (T1) needs to be increased to provide sufficient deflection to obtain a detectable signal afterwards. A five-fold increase (to 250ms) proved to be sufficient. With the magnetic brush in place the relationship between the deflection pulse length and the amplitude of vibration no longer follows the periodic relationship that the free magnet does.

Alternatively, the pulse length is increased until it is large enough for the brush to touch the container wall. When this occurs there is sufficient magnetic flux linkage between the magnet and the energised coil, via the carrier bridge that forms between the two, to make the magnetic attractive force exceed the mechanical restoring force of the spring thus keeping the magnet attracted to the vessel wall as long as the coil remains energised. The spring can then be released at any time by de-energising the coil; and this method was used to make the system operate with the pure developer.

Claims (29)

Claims:

1. An arrangement for detecting presence of a fluent material, comprising: a container for the material; a movable member disposed within said container; excitation means, disposed outside said container, for applying a force to said magnetic member; and detection means, disposed outside said container, for detectirig motion of said magnetic member resulting from the application of said force, and for thereby determining whether said material is present in the vicinity of said movable member.

2. An arrangement according to claim 1, wherein said container is formed of a nonmagnetic material; said movable member comprises a magnetic member; and said excitation means comprises electromagnetic excitation means, disposed outside said container, for applying a magnetic force to said magnetic member.

3. An arrangement according to claim 1 or 2, wherein said movable member is provided on a resilient member within said container, said movable member having a first position corresponding to the equilibrium position of said resilient member.

4. An arrangement according to claim 2 or 3, wherein said electromagnetic excitation means includes a coil mounted outside said container; and said detection means is adapted to be coupled to said coil for detecting signals generated in the coil due to said motion of said magnetic member.

5. An arrangement according to any of claims 1 to 4, wherein said excitation means includes means for applying a force to said movable member for a pre-determined period.

6. An arrangement according to claim 3, 4 or 5, wherein said resilient member comprises an elongate strip of flexible material, one end of the strip being fixedly attached to a sidewall of the container, and the opposite, free end being attached to said movable member.

7. An arrangement according to any of claims 3 to 6, wherein said first position is adjacent one or more walls of said container, and wherein, in the absence of said material from the vicinity of said movable member, said movable member is susceptible of substantially free movement.

8. An arrangement according to any of the preceding claims, wherein said container is substantially box-shaped and, in use, is positioned with its sides vertical; wherein said movable member is disposed adjacentthe base of said container; and wherein (1) said resilient member extends from adjacent the top of the container or (2) said resilient member extends horizontally such that said movable member is capable of movement in a horizontal or vertical plane.

9. An arrangement according to any of the preceding claims, wherein said force causes a maximum displacement of said movable member to a second position in the absence of said material from the vicinity of said movable member; and wherein said first and second positions define a first direction, and the axis of said coil is substantially parallel to or aligned with said first direction.

10. An arrangement according to any of the preceding claims, wherein said movable member comprises a permanent magnet or a material of high magnetic permeability.

11. An arrangement according to claim 9 or 10, wherein said detection means is enabled for a period corresponding to the decay time constant of the movable member and said resilient member from said second position to said first position.

12. An arrangement according to any of claims 5 to 11, wherein said detection means includes a delay circuit for setting the duration of said pre-determined period.

13. An arrangement according to any of claims 2 to 11, wherein said excitation means includes means for applying a time-varying force with frequency f to said movable member, where f is the fundamental frequency of said movable member and said resilient member.

14. An arrangement according to any of claims 2 to 13, wherein said detection means includes a switch, said coil being connected to an amplifier when said switch is in its NC position, and to a voltage supply when said relay switch is in its NO position.

15. An arrangement according to claim 14, wherein said switch comprises a relay.

16. An arrangement according to claim 14 or 15, wherein said detection means includes a demodulator circuit, coupled to the output of said amplifier, for generating a demodulated signal.

17. An arrangement according to claim 16, wherein said demodulator circuit includes a diode-resistor-capacitor circuit.

18. An arrangement according to claim 16 or 17, wherein said detection means includes a threshold detector, coupled to the output of said demodulator circuit, for comparing said demodulated signal with a pre-determined threshold.

19. An arrangement according to claim 18, wherein said detection means includes a flipflop, coupled to the output of said threshold detector and to a first monostable, the monostable being activated by the termination of said pre-determined period to supply an enabling pulse to said flip-flop; wherein the output of said flip-flop activates an indicating means if said demodulated signal exceeds said pre-determined threshold during the duration of said enabling pulse.

20. An arrangement according to claim 19, wherein said indicating means comprises an alphanumeric visual display, a LED or an audible indicator.

21. An arrangement according to claim 19 or 20, wherein said detection means includes one or more cascaded further monostables constituting said delay circuit and coupled to said first monostable; wherein said pre-determined period is initiated by the termination of said enabling pulse.

22. An arrangement according to any of claims 1 to 18, further including an input-output (I/O) port for coupling signals generated by said detection means to a software-controlled microcontroller or microprocessor.

23. An arrangement according to any of claims 2 to 22, including a plurality of movable members and a plurality of coils, the movable members being spaced from eachother at predetermined intervals, and each coil being positioned adjacent a respective members member; the arrangement thereby being adapted to determine partial and/or total consumption of said material from said container.

24. An arrangement according to any of the preceding claims, wherein said container comprises a user-replacable or permanently housed container in a xerographic or printing machine.

25. An arrangement according to any of the preceding claims, wherein said container comprises a toner hopper, an ink cartridge, or a fuser oil cartridge.

26. An arrangement according to any of the preceding claims, wherein said material comprises a toner powder, liquid ink or oil.

27. An arrangement according to any of the preceding claims, further including dispensing means, communicating with the interior of said container, for dispensing said material from said container at a pre-determined rate.

28. An arrangement according to claim 24, wherein said dispensing means includes a rotatable auger flight passing through a wall of the container at the base thereof.

29. An arrangement according to any of claims 2 to 28, wherein the or each coil comprises a multi-turn Helmholtz coil and/or the or each coil is provided with a ferrite or laminated high permeability core.