GB2203358A

GB2203358A - A toner density control device

Info

Publication number: GB2203358A
Application number: GB8730357A
Authority: GB
Inventors: Masayoshi Watanuki; Toshio Nakahara; Masanori Nagayama; Hajime Oyama; Yukio Noguchi
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1987-01-12
Filing date: 1987-12-31
Publication date: 1988-10-19
Also published as: DE3800248A1; FR2610424A1; GB8730357D0

Description

- 1 A TONER DENSITY CONTROL DEVICE 2203358 The present invention concerns

a toner density control device for use in copying machines, and more specifically, it relates to a toner density control device for controlling the toner density of developer composed of two ingredients, that is, toners and magnetic carriers.

In copying machines using developers composed of toners and magnetic carriers, toner density control devices have hitherto been employed for controlling the toner density, that is, the ratio of the toner to the carrier in the developer at a constant level. These toner density control devices are described, for Patent Laid-Open No. Sho 59-208566 example, in Japanese and Japanese Utility Model Laid-Open No. Sho 61- 46463. As the density detector for use in the density controlling device, there have been used an inductance detection device for measuring the magnetic permeability of the developer that varies depending on the change in the toner density, an optical reflectance detection device for detecting the reflectance of light from copied images in a recording paper.

However, the characteristics of these density detectors usually disperse, and in the inductance detection type toner density detector, its output is affected by the magnetic permeability of the carriers and the state of electrostatic charges in the carriers. Accordingly, standard developer must be charged in a reservoir after the assembling of a copying machine or on every replacement of the developer, to get the output from the density detector for this standard developer as the threshold value data for the density control and to set this data into the control device by the manual operation of a variable resistor, switch, etc. Further, in the case of the inductance detection type detector, it is necessary to wait to measure the output from the detector until the developer has been agitated to have sufficient electrostatic charges.

These procedures are troublesome and there are individual differences.

The. present invention has been accomplished in view of the foregoing problems and the object thereof is to provide a toner density control device capable of conveniently setting a reference density in a copying machine using a developer composed of toners and carriers.

The foregoing object of the present invention can be attained by a toner density control device comprising; a detection means for detecting toner density of a developer comprising toners and carriers, a first memory means for receiving and storing density data transmitted from said detection means at predetermined intervals, an averaging means for averaging a predetermined number of said density data received from said first memory means, a second memory means for storing the averaged density data, and T - 3 a control means for controlling the toner density in order that the toner density is kept at a density corresponding to the averaged density data stored in said second memory means. The foregoing object of the present invention can be attained also by a toner density control device comprising; a detection means for magnetically detecting toner density of a developer comprising toners and carriers, an agitation means for agitating the developer, a sampling means for sampling density data outputted from said detection means at predetermined intervals, a switching means for selecting either copying operation mode or toner density setting mode, a judging means for actuating said agitation means when the toner density setting mode is selected by said switching means, receiving two successive density data from said sampling means and judging whether a variation amount between said two density data is less than a predetermined value or not, a memory means for storing the density data received from said judging means.at the instance when the variation amount is judged to be less than said predetermined value by said judging means, and a setting means for setting the density data stored in said memory means as a threshold value for the density control.

The foregoing object of the present invention can further be attained by a toner density control device comprising; a detection means for magnetically detecting toner density of a developer comprising toners and carriers, an aaitation means for agitating the developer, a timer means for setting a period of time for which the developer is agitated, a switching means for selecting either copying operation mode or toner density setting mode, a memory means for storing a density data outputted from said detection means after the developer has been agitated by said agitation means for the period of time set by said timer means in case the toner densi ty setting mode is selected by said switching means, and a setting means for setting the density data stored in said memory means as the threshold value for the density control.

Description will be made for the present invention by way of its first and second embodiments specifically referring to the drawings.

The present invention is no way limited only to these examples but various modifications may of course be possible.

Figure 1 is a control block diagram in the first embodiment according to the present invention; Figure 2(a) is a flow chart for the first embodiment; Figure 2(b) is a flow chart for explaining the operation of a modification of the first embodiment; Figure 3 is a cross sectional view illustrating a developing device in the second embodiment according to the present invention; Figure 4 is a control block diagram in the second embodiment;- Figure 5 is a block diagram of the input circuit for the density detection means of the second embodiment; Figures 6 and 7 are flow charts for explaining the operation of the second embodiment; Figure 8 is a control block diagram of a modification of the second embodiment; Figure 9 is a flow chart for explaining the operation of the modification in the second embodiment; and Figure 10(a) and Figure 10(b) are views for explaining the induction detection type density detectors used in the density control device according to the present invention.

Explanation will be made more specifically to the first embodiment according to the present invention.

Figure 1 is a block diagram of the control system in the embodiment and Figure 2(a) is a flow chart. As can be seen from the figure, when reference developer is charged into a developing device and the density setting mode is started by switching the copying machine to the density setting mode, detection means 30 for detecting the toner density is actuated and the value detected from the detection means 30 is converted into digital signals by means of an analog-digital conversion means (hereinafter as A/D conversion means) 31 and read into a control means 32.

The control means 32 is connected with a display means 33, a memory means 34 for storing the values detected by the detection means 30 for a predetermined number of times and a toner supply means 35 respectively. Further as described later, an averaging means 36 for averaging the values stored in the memory means 34 is connected with a non-volatile memory means 37 for storing the averaged value.

Accordingly, as shown in Figure 2(a), when the copying machines is started (2-1), the reference developing powder is charged in the developing device as described above and the density setting mode is selected (2-2), operation elements required for the density setting are started (2-3). Then, the value detected by the detection means 30 as described above is read by way of A/D conversion means 31 to the control means 32 as sampling signals (2-4) and stored in the memory means 34 (2- 5). Since the detection values from the detection means 30 disperse more or less due to noises, etc., the values are read certain times at a certain interval and stored (2-6), and the sampling signals are averaged in the averaging means 36 (2-7) to reduce the dispersion. Further, the calculated average value is stored in the memory means 37 (2-8), and simultaneously, the completion of the density setting is displayed in the display means 33 (2-9).

In usual copying mode, the value stored in the non-volatile memory means 37 is used as the reference level, which is compared with the value detected by the detection means 30 to actuate a toner supply means 35 so that the toner density can be kept at the reference level.

The developer left unused for a long period of time after the production, has the degraded performance (main Q/M),_and accordingly, it is preferable to use the developer after agitating it for several minutes in the developing device. Since the above-mentioned performance affects the detection level of the detection means 30, the reference developer has to be agitated prior to the setting of the reference level.

Accordingly, as shown by the flow chart of Figure 2(b), after the start of the density setting control (2-3), the agitation means in the developing device is actuated first for a certain period by the timer means 38 (2-10), and then the toner density signal is sampled.

In the flow chart shown in Figure 2(b), the identical with those explained in Figure 2(a) carry reference numerals and detailed descriptions are omitted.

Next, description will be made to the second embodiment according to the present invention.

Figure 3 is a cross sectional view illustrating a developing device, Figure 4 is a block diagram showing the entire control system, Figure 5 is a block diagram showing the input circuit of the density detection means, Figure 6 portions the same therefor is a flow chart of the toner density setting control mode and Figure 7 is a flow chart of the copying operation control mode.

In Figure 3, a developing device 1 includes a developing roller 2, a pair of paddling rollers 3 and 4, an agitation roller 5, an agitator 6, a toner supply pipe 7, etc. as in the known manner. Detection means for detecting the mixing ratio of developer 8 composed of toners and magnetic carriers is disposed on the lower portion of the developing device 1. Further, the developing roller 2, paddling rollers 3 and 4, agitation roller 5 and agitator 6 constitute an agitation means for agitating the developer 8.

The detection means 9 magnetically detects the mixing ratio of the toners to the magnetic carriers, and as shown in Figure 5, the analog signal according to the mixing ratio detected by the detection means 9 is inputted by way of an analoq/digital (A/D) conversion circuit 10 to a central processing unit (CPU) 11.

By the way, the amount of electrostatic charges of the developer 8 left unused for a long period of time is small and gradually increase along with the agitation. The amount of the electric charges affects the output of the magnetic detection means 9. The output of the magnetic detection means 9 is reduced when the amount of the electrostatic charges is small even if the toner density of the developer is the same. Accordingly, the density setting operation has to be conducted in a settled state of electrostatic charges.

In view of the above, in the density control device of the present embodiment, the density data from the detection means 9 are sampled at certain intervals by the CPU 11 as the sample memory means, and when the variation amount between two successive density data goes below the predetermined value, the density data at that moment is stored in a nonvolatile memory means (as described later).

Specifically, when the density data are outputted as D0j, D ly the density variation is determined as below by the moving averaging method to obtain a threshold value D D 0 + D 1 + D 2 + D 3 4 D 4 + D 5 + D 6 + D 7 4 D 4 + D 5 + D 6 + D 7 4 D 8 + D 9 + D 10 + D 11 4 >AD... (1) - <ADA (2) When the inequality (2) is calculated after the - 10 inequality (1), D, presented by the following formula:

D 8 + D 9 + D 10 + D 11 = D 4 is stored as the threshold value data. An accurate density control is obtainable by using the averaged value as described above.

In the moving averaging method described above, the inequalities (1) and (2) may be replaced with the following inequalities (3) and (4) respectively.

D 0 + D 1 + D 2 + D 3 D 2 + D 3 + D 4 + D 5 >AD... (3) 4 4 D 2 + D 3 + D 4 + D 5 D 4 + D 5 + D 6 + D 7 <AD... (4) 4 4 Further, CPU 11 as shown in Figure 4 is connected with an operation section 12, a switching means 13 comprising a mode change-over switch for selecting the usual A copying operation mode or the toner density setting modep a non-volatile memory means (RAM) 15. a driver 19 for driving a main motor 16p a developing motor 17 and a toner supplying motor 18 respectively.

Description will then be made to the operation of the above-mentioned embodiment while referring to the flow chart shown in Figure 6.

At first, the toner density setting mode is set by the switching means 13 (6-1). In this mode, usual copying operation is not conducted. Under this state, the density setting mode is started by the key operation in the operation section 12. Those portions required for the agitation of the developer are actuated by this operation. In the present embodiment, if only the developing motor 16 is actuated, agitation means 2, 3, 4, 5, 6 in the developer device 1 are rotated by way of driving transmission system (6-3), and the developer 8 is agitated.

Prior to starting the agitating operation, the lower limit of the density is set through CPU 11 (6-2). Then, the density data (Dx) of the developer 8 detected by the detection means 9 during the agitating operfation are sampled by the CPU 11 (6-4). The sampling is carried out every 4 - 5 seconds in the case of color copying.

The difference AD between the average value Rn of density data D 0 - D n outputted from the detection means 9 and the last average value Rn-1 is calculated (6-5), and if the difference AD goes less than the predetermined value AD (6-6), the average value Rn at this instance is stored by the CPU 11 in the non- volatile memory means 15 (6-7) as the density control threshold value D and the agitation stops (6-8). In this case, the end of the mode may preferably be displayed at the display portion of the operation section 12.

After the toner setting mode has been ended, the copying machine is returned to the copying operation mode by way of the switching means 13.

The operation of the copying operation mode is explained referring to the flow chart shown in Figure 7.

When the mode is started by depressing the copy start button of the operation section 12 (7-1), those portions required for the copying operation are actuated (7-2). Then, the toner density data (Dx) sampled during copying operation (7-3) are compared with the threshold value data (D) stored in the non-volatile means 15 by the CPU 11 (7-4), and if D > Dx, the toner supply motor 18 is actuated to supply the toners by the toner supply pipe 7 (7-5). On the other hand, if D < Dx, the supply of the toners is interrupted (7-6). In this way, the density control is carried out. Then, to stop the copying operation (7-7), the portions required for the copying operation are interrupted (7-8).

In the second embodiment described above, although the density data at the instance that the developer is 71 13 - 1 agitated until the variation of the toner density is less than the predetermined value, is used as the threshold value for the density control, it may alternatively be so adapted that the developer is agitated for a certain period of time and the density data at that instance is used as the threshold level for the density control. In this case, a timer means 14 for setting a period of time for which the developer is agitated is connected to the CPU as shown in Figure 8. The operation of the density control device in this case is explained referring to the flow chart shown in Figure 9.

At first, the control system is set to the toner density setting mode by the switching means 13 (9-1). In this mode, usual copying operation is not conducted. Under the state, the density setting mode is started by the key operation in the operation section 12. By this operation, those portions required for the agitation of the developer are actuated.

Simultaneously with the agitating operation, the timer means 14 is actuated (9-3). Since the charqed state of the developer 8 is settled after the agitation has been continued for a certrain period of time, the timer means 14 is set so that the agitation is continued for a predetermined time. The period required for agitation is, for instance, from 1 to 3 minutes in the case of black and white copy, from 1 to 3 minutes in the case of color copy at low humidity and from 5 to 10 minutes for color copy at high humidity.

14 - When the timer means 14 detects that the predetermined period of time has been elapsed (9-4), the density data is sampled and stored as the threshold value data (D for density control in the non-volatile memory means 15 (9-5) and the agitation is interrupted (9-6).

Description will then be made to the inductance detection type density detector that can be used for the density detection device according to the present invention while referring to Figures 10(a) and (b).

Figure 10(a)'is a cross sectional view illustrating a portion of a developing device and Figure 10(b) is an electrical circuit of the density detector.

In Figure 10(a), a developing device 52 is disposed at the outer circumference of a photosensitive drum 52. In the developing device 52, a developer 54 composed of resin-coated iron powder (carriers) and toners charged in the lower portion of a developing reservoir 53 is paddled up by means of a first paddling sleeve 57 having two magnets 55 and 56 secured to the inside thereof and a second paddling sleeve 59 having two magnets 58a and 58b secured to the inside thereof and then transferred to a developing sleeve 62 having two magnets 60 and 61 disposed to the inside thereof.

Then, after being deposited on the photosensitive drum 51 by means of the developing sleeve 62 to visualize the electrostatic latent images, the developer 54 having the reduced toner density is separated from the developing sleeve 62 by a separator 63 and then fallen on an agitation 1 screw 64. Then, the fallen developer is agitated uniformly with toners supplied from a toner supply pipe 65 by way of a toner supply roller 66.

Further, in the developing device 52, a toner density detection hopper 67 that causes the developer 54 separated from the developing sleeve 62 by the separator 63 to pass partially (or wholly) is disposed, and a coil 68 is disposed around the cylindrical outer circumference of the hopper 67. On the other hand, a substrate 71 for mounting other members including capacitors 69 and 70 that constitute an LC oscillator (described later) together with the coil 68 is mounted to the outer wall of the developing reservoir 53, and the coil 68 is connected with the capacitors 69 and 70.

The LC oscillator 71 comprises, as shown in Figure 10(b), the coil 68, the oscillating capacitors 69 and 70, a DC component cut-off capacitor 72, a transistor 73 and resistors 74, 75, 76 and 77, and it oscillates at a frequency depending on the inductance of the coil 68 and the capacitance of the capacitors 69 and 70.

Accordingly, since the inductance of the coil 68 varies depending on the ratio of the toners to the carriers of the developer 54, the LC oscillator 71 outputs the toner density signal of a frequency depending on the toner density of the developer 54.

That is, the toner density can be controlled by the comparison between the oscillation frequency f 0 determined by the inductance L 0 of the coil 68 and the capacitance C of the capacitors 69 and 70 when the reference - 16 developer 54 is charged and the frequency f detected during copying operation, but the value f 0 depends on every copying machine since there are dispersions in the values L 0 and C.

As has been described above, in the density control device according to the present invention, the threshold value for the density control can be set accurately and automatically without being influenced by the characteristics of the developer, electro static charaes and the characteristics of the density detector.

The present invention is no way restricted only to the embodiments described above but various modifications are of course possible. For instance, the density detector may be of such a type that measures the electroconductivity of the developer, measures specific gravity of the developer, or measures the reflection of light from a printed recording paper.

Claims

WHAT IS CLAIMED IS:.

1. A toner density control device comprising; a detection means for detecting toner density of a developer comprising toners and carriers, a first memory means for receiving and storing density data transmitted from said detection means at predetermined intervals, an averaging means for averaging a predetermined number of said density data received from said first memory means, a second memory means for storing the averaged density data, and a control means for controlling the toner density in order that the toner density is kept at a density corresponding to the averaged density data stored in said second memory means.

2. The device of claim 1, wherein the density data outputted from the detection means is converted into digital signals by an A/D converter and then supplied to the first memory means.

3. The device of claim 1 or 2, wherein the second memory means comprises a non-volatile memory.

4. The device of any one of claims 1 to 3, wherein the averaging means comprises a microcomputer.

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5. A toner density control device comprising; a detection means for magnetically detecting toner density of a developer comprising t oners and carriers, an agitation means for agitating the developer, a sampling means for sampling density data outputted from said detection means at predetermined intervals, a switching means for selecting either copying operation mode or toner density setting mode, a judging means for actuating said agitation means when the toner density setting mode is selected by said switching means, receiving two successive density data from said sampling means and judging whether a variation amount between said two density data is less than a predetermined value or not, a memory means for storing the density data received from said judging means at the instance when th variation amount is judged to be less than said predetermined value by said judging means, and a setting means for setting the density data stored in said memory means as a threshold value for the density control.

6. The device of claim 5, wherein each of said two successive data is an average value of plural successive density data.

2 - 19

7. The device of claim 5, wherein the density data outputted from the detection means is converted into digital signals by an A/D converter and then supplied to the sampling means.

8. The-device of any one of claims 5 to 7r wherein the memory means comprises a non-volatile memory.

9. The device of claim 5, wherein the judging means.comprises a microcomputer.

10. A toner density control device comprising; a detection means for magnetically detecting toner density of a developer comprising toners and carriers, an agitation means for agitating the developer, a timer means for setting a period of time for which the developer is agitated, a switching means for selecting either copying operation mode or toner density setting mode, a memory means for storing a density data outputted from said detection means after the developer has been agitated by said agitation means for the period of time set by said timer means in case the toner density setting mode is selected by said switching means, and a setting means for setting the density data stored in said memory means as the threshold value for the density control.

11. The device of claim 10, wherein the density data outputted from the detection means is converted into digital signals by an A/D converter and then supplied to the memory means.

12. The device of claim 10 or 11, wherein the memory means comprises a non-volatile memory.

13. A toner density control device, substantially as herein described wit. h referen-ce to Figures 1 to 2b, or Figures 3 to 9 of the accompanying drawings.

Published 1988 at The Patent Office. State I-louse, 66.71 Iligh Holborn. London WC1R 4TP, Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Miltiplex techniques ltd, St Mary Cray, Kent. Con. 1187.

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