WO2009036504A1

WO2009036504A1 - Toner concentration determination and replenishment systems

Info

Publication number: WO2009036504A1
Application number: PCT/AU2008/001382
Authority: WO
Inventors: Alvin George Chowles; Trevor Donald Nation; Robert John Thompson
Original assignee: Research Laboratories Of Australia Pty Ltd
Priority date: 2007-09-20
Filing date: 2008-09-18
Publication date: 2009-03-26

Abstract

A toner particle concentration determination device has a pair of spaced apart electrically conducting plates (34) such as concentric cylinders to be extended into a toner, the particle concentration of which is to be determined. An electronic arrangement (45) measures the electrical capacitance between the plates hence enables determination of toner particle concentration. A liquid toner recycling and replenishment system for an printer includes a make up arrangement to supply make up concentrated toner particles and carrier liquid from respective storage tanks (41, 43) to a toner tank (30) and uses a toner particle concentration determination device (32) to control supply of toner particles and carrier liquid from the respective storage tanks to the toner tank to maintain the toner particle concentration in the toner tank at a selected level. A method of non-destructive testing of toner particle concentration is also described.

Description

TONER CONCENTRATION DETERMINATION AND REPLENISHMENT SYSTEMS DESCRIPTION

FIELD OF INVENTION

This invention relates to copiers and printers and more particularly to systems for measuring particle concentration of consumables and recycling systems for consumables of such systems.

BACKGROUND OF THE INVENTION

The invention will generally be discussed in relation to liquid toners or developers for electrostatic printing systems, but the invention is not so limited and can also be used for inks used in other printing processes such as inkjet systems where recycling of ink is possible.

Liquid toners, developers or inks are used in some printing systems such as electrostatic printers, inkjet printers and electrostatic inkjet printers. It is desirable where possible to recycle toner for reuse to avoid wastage and to minimise toner consumption, but it is necessary to know what concentration of the insoluble marking particles of the toner is present in a toner tank to ensure consistent results when such a recycled toner is used again.

Liquid toners or developers generally comprise a non-conductive or insulative carrier liquid and toner particles suspended in the carrier liquid. The amount of particles for a particular printer can determine the quality of printing and hence it is desirable to know what particle concentration is present in a toner or ink.

For the purpose of this specification, the usage of the term toner is intended to include liquid developers, liquid toners and liquid inkjet inks that comprise solid particles insoluble in the carrier liquid.

Liquid developers have generally utilized low viscosity liquids and low concentration of the solids content, that is, of marking particles. These traditional toners and associated process systems may be termed low viscosity toner ( LVT) systems. Generally, LVT systems utilise toners with low viscosities, typically 1 to 3 mPa.s. and low volumes of solids, typically 0.5 to 2% by weight. More recently, however, highly concentrated liquid toner systems utilising toner concentrations of up to 60% by weight and viscosities of up to 10,000 mPa.s, have been disclosed. This system of developing electrostatic latent images with these viscous and highly concentrated liquid toner systems have been termed high viscosity toner (HVT) systems. LVT system have traditionally used an optical sensing device including a light emitting element for emitting a light beam onto the liquid developer and a light sensing element receiving the optical signal transmitted through the developer as a method of determining toner particle concentrations, and hence facilitating the control of toner particle concentration through a regulation means or as part of a recycling system.

In such an optical sensing device, the light sensing element generates a voltage signal proportional to the intensity of the light beam received by the light sensing element, which corresponds to a density of the liquid type developer existing between the light emitting element and the light sensing element which receives a light beam emitted from the light emitting element after passing through the liquid developer. Therefore, the weaker the light beam received by the light sensing element, the higher the light absorption by the toner, hence the higher particle concentration of the liquid developer.

Additionally, concentration detection of a liquid developer by an optical sensing device is not stable over a long period of operation due to variations in adherence of the particles in the liquid developer to the light sensing element.

The use of this optical method is limited to very dilute liquid developers with a typical concentration of solid content of below 2%, due to the significant reduction in intensity of the transmitted light, and for concentrated developers, the intensity is below the detection limit of the light sensing element. Therefore, the use of HVT systems makes the use of optical sensing devices impractical due to the concentrated nature of the toners.

It is the object of this invention therefore to provide a toner recycling system for electrostatographic or inkjet printers and a method of determining particle concentration for such systems.

BRIEF DESCRIPTION OF THE INVENTION

In one form the invention comprises a toner particle concentration determination device comprising a pair of spaced apart electrically conducting plates to be extended into a toner, the particle concentration of which is to be determined, and an electronic arrangement to measure the electrical capacitance between the plates and hence enable determination of toner particle concentration.

The pair of plates can comprise concentric cylinders and the capacitance is measured between the cylinders. The concentric cylinders can be in a flow through housing and toner is pumped from the toner tank through the flow through housing and back to the toner tank or they can be within the toner tank. The concentric cylinders can comprise inner and outer cylinders and the electronic arrangement can be at least partially within the inner cylinder.

The inner cylinder can be of lesser length than the outer cylinder whereby to avoid edge effects.

The inner and outer cylinders can be separated by a spacer arrangement extending across each end thereof and the outer cylinder can comprise a mesh extending across each end thereof.

The pair of spaced apart electrically conducting plates or the inner and outer cylinders can be spaced apart by a distance of from 0.1 to 10 mm, preferably spaced apart by a distance of from 1 to 5 mm, or more preferably spaced apart by a distance of 3 to 5 mm, preferably 3 mm.

It will be seen that by this invention there is provided a system which enables a non-destructive method of testing the concentration of particles within a toner.

The present invention can be used to measure particle concentration in both HVT and LVT systems.

Additionally, by this invention there is provided an analytical device which enables a non-destructive method of measuring the capacitance of a liquid toner. Further, other electrical characteristics of liquid tones such as resistivity for example, may also be measured.

In an alternative form, therefore, the invention is said to reside in a liquid toner recycling and replenishment system for an electrostatographic printer, the system including a toner tank, a supply system to supply liquid toner to a print engine, a recovery system to return unused toner from the print engine to the toner tank and a make up arrangement to supply concentrated toner particles and carrier liquid from respective storage tanks to the toner tank, characterised by a toner particle concentration determination device associated with the toner tank and a control arrangement associated with the toner particle concentration determination device to control supply of toner particles and carrier liquid from the respective storage tanks to the toner tank to maintain the toner particle concentration in the toner tank at a selected level.

Preferably, the toner tank includes an agitator arrangement to maintain the toner particle concentration in the toner tank homogenous.

In one embodiment, the toner particle concentration determination device comprises a pair of spaced apart electrically conducting plates to extend into the toner and an electronic arrangement to measure the electrical capacitance of the toner between the plates and hence enable determination of toner particle concentration which is directly linked with the electrical capacitance .

The pair of plates can comprise concentric cylinders and the capacitance can be measured between the cylinders. The concentric cylinders can be in a flow through housing and toner is pumped from the toner tank through the flow through housing and back to the toner tank or they can be within the toner tank.

The concentric cylinders can comprise inner and outer cylinders and the electronic arrangement can be at least partially within the inner cylinder.

In a further form the invention comprises a method of non-destructive testing of toner particle concentration comprising the steps of; passing a toner whose particle concentration is to be determined between a pair of electrically conductive plates; applying a known voltage between the plates; determining the capacitance between the plates; and thereby determining the particle concentration using the calibration curve between the capacitance and the particle concentration.

Preferably the known voltage is pulsed with a triangular waveform to measure both the capacitive (imaginary) and resistive (real) components of the impedance between the plates. It would be understood by those skilled in the art that an alternative waveform could be used including that of a sine or square wave for example.

Preferably the known voltage is pulsed with reversing polarity, that is, the waveform is symmetrical in voltage around zero volts. This is to avoid unwanted deposition or plate-out of the marking particles on the conducting plates. Preferably a triangular voltage signal is applied between the plates and the related in-series current is a measured signal wherein a first sample of the measured signal is taken at the exact zero-crossing point of the triangle in the falling half-cycle which sample represents the capacitance value of the device and hence the permittivity of the material between its cylinders and second sample is taken to define the inclination of the return signal and hence the conductance of the material between the cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

This generally describes the invention, but to assist with understanding reference will now be made to the accompanying drawings which show preferred embodiments of the invention.

In the drawings:

Figure 1 shows an embodiment of the toner concentration device according to the present invention;

Figure 2 shows a cross sectional view of the device shown in Figure 1; Figure 3 shows a top view of the device of Figure 1;

Figure 4 shows a first embodiment of toner replenishment system according to the present invention;

Figure 5 shows an alternative embodiment of toner replenishment system according to the present invention; Figure 6 shows an alternative schematic toner replenishment system for electrostatic printer incorporating a flow-through system for toner recycling;

Figures 7 to 10 show graphs of dielectric constant and capacitance against various characteristics to show the high accuracy of detecting solid content with the device of the present invention; and

Figure 11 shows a system block diagram of an electronic circuit of one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Looking at Figure 1 to 3, it will be seen that one embodiment of a toner concentration determination device 1 comprises an upper housing 2 and a lower housing 3 which are held together by screws 4. Clamped between the upper and lower housing components are an outer cylinder 12 and an inner cylinder 14 spaced apart by spacers 16 at each end to give a gap between the inner and outer cylinders as indicated by the arrow 18. The gap 18 is between 0.1 to 10 mm, preferably from 1 to 5 mm, or more preferably 3 to 5 mm and preferably 3 mm. In this illustrated embodiment, the inner cylinder has an outer diameter of 16 mm and the outer cylinder has an inner diameter of 22 mm. The length of the device in this embodiment is 21 mm. A mesh screen 27 is provided at each end of the outer cylinder to prevent any oversized toner particles and other contaminants from passing through between the inner and outer cylinders and causing anomalous results. A toner inlet 26 is provided at the lower end of the device and a toner outlet 28 at the upper end of the device.

An electronic arrangement 22 to at least part process the capacitance signal is placed within the inner cylinder 14. An electrical connection 23 extends from the electronic arrangement 22 to the inner cylinder and an electrical connection 25 extends to the outer cylinder 12 via aperture 29 in the upper housing and connects to the outer cylinder 12 between the upper housing 2 and the lower housing 3 at connection 19. An electrical signal as discussed below is applied between the outer cylinder 12 and inner cylinder 14.

Toner is allowed to flow through the unit 1 as shown by flow lines 20 between the inner cylinder 14 and the outer cylinder 12. The electronic arrangement 22 processes the measured capacitance signal between the inner cylinder 14 and the outer cylinder 12 and the electrical capacitance is used to determine particle concentration. The signal from the electronic arrangement 22 is sent by line 24 to controller 45 (see Figure 4) for instance.

Capacitance between the inner and outer cylinders is a measure of the dielectric properties of the bulk toner and the ability of the cylinder plates to acquire charge upon voltage application. The capacitance value depends on the geometry of the sensor arrangement, dielectric properties of the carrier liquid, the toner particles and other ingredients such as charge control agents, dispersants and the like. The capacitance value as determined with the present invention strongly depends on particle concentration. To measure the capacitance, a known voltage is applied between the plates or cylinders and the resulting capacitance is measured. To reduce the effect of irreversible particle deposition onto the plates or cylinders the voltage is pulsed with reversing polarity. A triangular waveform is used to measure both the capacitive (imaginary) and resistive (real) components of the impedance in the device.

A triangular signal is sent to the device's outer cylinder and the current from inner cylinder to ground is measured by the circuit inside the inner cylinder. A first sample of this return signal is taken at the exact zero-crossing point of the triangle in the falling half-cycle. This sample represents the capacitance value of the device and hence the permittivity of the material between its cylinders. A second sample is taken to define the inclination of the return signal and hence the conductance of the material between the cylinders.

Figure 4 shows one embodiment of a toner management system for an electrostatic printer according to the present invention. In this embodiment a toner tank 30 has toner 31 inside it and a toner concentration measuring device 32 comprising a pair of electrically conductive plates 34 extending into the toner.

Toner is taken for use in a printer via line 35 and used toner is returned by line 37. A stirrer 39 is used to keep the toner 31 in the tank 30 in an agitated and homogenous condition. The returned toner may change the concentration of particles in the tank to outside a desirable usage range for a particular printer and hence, it is necessary to adjust the concentration of toner particles from a toner particle concentrate in tank 41. It may also be necessary from time to time to restore the toner solid content by adding carrier liquid and this can be supplied from tank 43.

The toner concentration measuring device 32 provides a capacitance related signal via line 32a to controller 45 and the controller 45 determines the particle concentration and operates valves 47 for the toner concentrate and 49 for the carrier liquid to supply these to the tank as necessary to maintain the toner concentration at an optimal level. The stirrer 39 ensures flow around the toner tank and between the plates 34 to provide uniform distribution of the toner particles in the toner tank for maximum accuracy of measurement.

Figure 5 shows an alternative embodiment of a toner management system for an electrostatic printer according to the present invention. In this embodiment the components similar to those of Figure 4 will have the same reference numerals.

In this embodiment a toner tank 30 has toner 31 inside it and a toner concentration measuring device 33 comprising outer and inner concentric cylindrical electrodes 36 which extend into the toner. Toner is taken for use in a printer via line 35 and used toner is returned by line 37. A stirrer 39 is used to keep the toner 31 in the tank 30 in an agitated and homogenous condition. In this embodiment at least some of the electronics to measure the capacitance between the concentric cylindrical electrodes 36 can be positioned within the inner cylinder.

The returned toner may change the concentration of particles in the tank to outside a desirable usage range for a particular printer and hence, it is necessary to adjust the concentration of toner particles from a toner particle concentrate in tank 41. It may also be necessary from time to time to restore the toner solid content by adding carrier liquid and this can be supplied from tank 43.

The toner concentration measuring device 33 provides a capacitance related signal via line 33a to controller 45 and the controller 45 determines the particle concentration and operates valves 47 for the toner concentrate and 49 for the carrier liquid to supply these to the tank as necessary to maintain the toner concentration at an optimal level. The stirrer 39 ensures flow around the toner tank and through the toner concentration measuring device 33 to provide uniform distribution of the toner particles in the toner tank for maximum accuracy of measurement. Figure 6 shows an alternative arrangement of toner management system for an electrostatic printer according to the present invention. In this embodiment the components similar to those of Figure 4 will have the same reference numerals.

hi this embodiment a toner tank 30 has toner 31 inside it. A pump 46 draws out toner 31 from the tank 30 through pipe 42 and the toner passes through a toner concentration measuring device 44 before being returned to the tank 30. Toner is taken for use in a printer via line 35 and used toner is returned by line 37. A stirrer 39 is used to keep the toner 31 in the tank 30 in an agitated and therefore in a homogenous condition.

The toner concentration measuring device 44 is of the type shown in Figures 1 to 3.

The returned toner may change the concentration of particles in the tank to outside a desirable usage range for a particular printer and hence it is necessary to adjust the concentration of the toner particles by adding from a toner particle concentrate in tank 41. It may also be necessary from time to time to restore the toner solid content by adding carrier liquid and this can be supplied from tank 43.

The toner concentration measuring device 44 provides a capacitance related signal to controller 45 and the controller 45 determines the particle concentration and the controller operates valves 47 for the toner concentrate and 49 for the carrier liquid to supply these to the tank as necessary to maintain the toner concentration at an optimal level.

Figure 7 shows a plot of dielectric constant versus solid content for a paraffin oil based HVT toner. The values obtained for the dielectric constant for various dilutions of a black paraffin oil based HVT toner are shown. The dielectric constant varied between about 2.1 to 2.6 for toner solid content values of about 15 to 27%. The dielectric constant increases as the solid content increases.

Figure 8 shows capacitance curves for tests of two types of carrier liquid based HVT toner. A liquid paraffin HVT toner (lpo toner) is represented with square markings and a silicone fluid based HVT toner with diamond markings. It can be seen that each type of carrier liquid has a different capacitance but each have substantially straight line graphs.

Figure 9 shows test results of the capacitance as measured for a typical four colour HVT toner set. It will be seen that while each toner has a different capacitance range each has a substantially straight line graph which indicates that concentration can be determined accurately from the capacitance at any toner concentration within the sensor solid content range. Figure 10 shows test results for a low viscosity toner (LVT) and illustrates a graph of solid content vs voltage output signal which is measured from the capacitance as discussed below.

The electronic circuit of this embodiment includes a triangle wave generator block 50, an inner cylinder block 60, a sample timing block 70 and a sampling block 80 and from these can be generated a capacitance signal 83 and a conductance signal 85.

In the triangle wave generator block 50 a highly linear, frequency stable triangle voltage waveform is generated and applied to the outer cylinder electrode 55. The method used to derive this voltage is to start with a crystal oscillator 51 and divide the frequency in a divider 52 to a pre-determined value. An integrator 53 is an operational amplifier configured to produce the waveform. The waveform is then applied to the outer cylinder via line 54 and also to the sample timing block 70 as discussed below.

In the inner cylinder block 60 the inner cylinder electrode 61 is wired to the input of a current-to-voltage (trans-resistance) amplifier 62 on a circuit board which is mounted inside the inner cylinder electrode. It is preferably mounted this way to shield the sensitive circuit from extraneous signals and deliver an amplified output signal from a low impedance source that is unaffected by environmental electrical noise. The amplified signal from the inner cylinder is provided to the sampling block 80 on line 63. The signal from the current amplifier is then processed by a circuit external to the inner cylinder.

The triangular waveform voltage signal from the integrator 53 is also provided to the sample timing block 70 via line 54a. The process of sampling the signal received at the inner electrode involves sampling the current signal at two set points on the triangle waveform, one at the zero crossing point on the falling half-cycle, the other at a selected fixed voltage near the peak of the negative half-cycle. In the sample timing block 70 a zero crossing detector 71 detects the time of the zero crossing point from the signal on line 54 and provides this time to a first pulse generator 72. A time signal from the first pulse generator 72 is transferred to the sampling block 80. Also in the sample timing block 70 a fixed level detector 73 detects the time of the selected fixed voltage near the peak of the negative half-cycle and provides that time signal to a second pulse generator 74. A time signal from the second pulse generator 72 is transferred to the sampling block 80.

In the sampling circuit 80 the samples of capacitance and conductance taken need to be as close as possible to the instantaneous value of the current at the selected voltage points on the triangle waveform, so a pulse as short as practical is generated for each of the sampling signals in the first and second pulse generators as discussed above. The two samples are taken by standard sample-and-hold circuits 81, 82 respectively, by closing a voltage controlled switch for the sampling time and storing the charge on a capacitor between samples. The sample and hold circuit 81 uses the time pulse generated by the first pulse generator 72 and applies it to the amplified signal on line 63. The voltage on line 83 representing the capacitance of the sensor is the magnitude of voltage output from the zero crossing sample-and hold circuit 81.

The sample and hold circuit 82 uses the time pulse generated by the second pulse generator 72 and applies it to the amplified signal on line 63. The voltage 85 representing the conductance is obtained by subtracting the zero crossing sample-and-hold voltage 83 from voltage on line 86 from the sample and hold circuit 82, using a differential or instrumentation amplifier 84.

The equation for the current flowing between the plates or cylinders, when voltage signal changes linearly with time, such as, for example, in a triangular waveform, is represented by (1):

Where C_τ and R_τ are toner capacitance and resistance respectively and U(t) is a time varying voltage applied to the plates.

In the case where voltage signal changes linearly with time, U(t) = cct + U(t = 0) and dU = a = constant , equation (1) enables one to determine both capacitance (2) and resistivity (3) of a dt toner sample from tangents to the current and voltage transient curves in the linear regions:

dt

A f (3) dt

where, pr is toner resistivity, A is electrode area and L is the gap between the plates or cylinders.

From the values of the samples of capacitance and conductance, a determination of particle concentration may be made using look up tables or calculated from empirical formulae for a given toner type. It can be appreciated that changes to any of the above embodiments can be made without departing from the scope of the present invention as defined by the claims and that other variations of the specific construction disclosed herein can be made by those skilled in the art without departing from the invention.

Claims

1. A toner particle concentration determination device comprising a pair of spaced apart electrically conducting plates to be extended into a toner, the particle concentration of which is to be determined, and an electronic arrangement to measure the electrical capacitance between the plates and hence enable determination of toner particle concentration.

2. A toner particle concentration determination device as in Claim 1 wherein the pair of plates comprise concentric cylinders and the capacitance is measured between the cylinders.

3. A toner particle concentration determination device as in Claim 2 wherein the concentric cylinders are mounted in a flow through housing.

4. A toner particle concentration determination device as in Claim 2 wherein the concentric cylinders comprise inner and outer cylinders and the electronic arrangement is at least partially within the inner cylinder.

5. A toner particle concentration determination device as in Claim 4 wherein the inner cylinder is of lesser length than the outer cylinder whereby to avoid edge effects.

6. A toner particle concentration determination device as in Claim 4 wherein the inner and outer cylinders are separated by a spacer arrangement extending across each end thereof.

7. A toner particle concentration determination device as in Claim 3 comprising a mesh extending across ends of the concentric cylinders.

8. A toner particle concentration determination device as in Claim 4 wherein the inner and outer cylinders are spaced apart by a distance of from 0.1 to 10 mm, preferably spaced apart by a distance of from 1 to 5 mm, or more preferably spaced apart by a distance of 3 to 5 mm, preferably 3 mm.

9. A liquid toner recycling and replenishment system for an electrostatographic printer, the system including a toner tank, a supply system to supply liquid toner to a print engine, a recovery system to return unused toner from the print engine to the toner tank and a make up arrangement to supply make up concentrated toner particles and carrier liquid from respective storage tanks to the toner tank, characterised by a toner particle concentration determination device associated with the toner tank and a control arrangement associated with the toner particle concentration determination device to control supply of toner particles and carrier liquid from the respective storage tanks to the toner tank to maintain the toner particle concentration in the toner tank at a selected level.

10. A liquid toner recycling and replenishment system as in Claim 9 wherein the toner tank includes an agitator arrangement.

11. A liquid toner recycling and replenishment system as in Claim 9 wherein the toner particle concentration determination device comprises a pair of spaced apart electrically conductive plates to extend into the toner and an electronic arrangement to measure the electrical capacitance of the toner between the plates hence enable determination of toner particle concentration.

12. A liquid toner recycling and replenishment system as in Claim 11 wherein the pair of plates comprise concentric cylinders and the capacitance is measured between the cylinders.

13. A liquid toner recycling and replenishment system as in Claim 12 wherein the concentric cylinders are in a flow-through housing and toner is pumped from the toner tank through the flow- through housing and back to the toner tank.

14. A liquid toner recycling and replenishment system as in Claim 12 wherein the concentric cylinders are within the toner tank.

15. A liquid toner recycling and replenishment system as in Claim 12 wherein the concentric cylinders comprise inner and outer cylinders and the electronic arrangement is at least partially within the inner cylinder.

16. A liquid toner recycling and replenishment system as in Claim 15 wherein the inner cylinder is of lesser length than the outer cylinder whereby to avoid edge effects.

17. A liquid toner recycling and replenishment system as in Claim 12 wherein the inner and outer cylinders are separated by a spacer arrangement extending across each end thereof.

18. A liquid toner recycling and replenishment system as in Claim 12 comprising a mesh extending across the concentric cylinders.

19. A liquid toner recycling and replenishment system as in Claim 11 wherein the pair of spaced apart electrically conducting plates are spaced apart by a distance of from 0.1 to 10 mm.

20. A liquid toner recycling and replenishment system as in Claim 12 wherein the concentric cylinders are spaced apart by a distance of from 0.1 to 10 mm.

21. A method of non-destructive testing of toner particle concentration comprising the steps of: passing a toner whose particle concentration is to be determined between a pair of electrically conductive plates; applying a known voltage between the plates; determining the capacitance between the plates; and thereby determining the particle concentration.

22. A method of non-destructive testing as in Claim 21 wherein the known voltage is pulsed with reversing polarity.

23. A method of non-destructive testing as in Claim 21 wherein the known voltage is pulsed with a triangular waveform to measure both the capacitive (imaginary) and resistive (real) components of the impedance between the plates.

24. A method of non-destructive testing as in Claim 23 wherein the known voltage with the triangular waveform is applied between the plates and an in-series current is a measured signal wherein a first sample of the measured signal is taken at the exact zero-crossing point of the triangle in the falling half-cycle which sample represents the capacitance value of the device and hence the permittivity of the material between its cylinders and second sample is taken to define the inclination of the return signal and hence the conductance of the material between the cylinders.