JPH0157790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a heating type fixing device used in an electrophotographic printer or an electrostatic recording printer.

(2) Background of the technology Electrostatic recording type and electrophotographic printers have excellent print quality and printing speed, and their operation is extremely quiet, making them particularly suitable as output printers for office computers. There is an alternative to line printers.

For example, in an electrophotographic printer, a photosensitive plate is charged to give it photosensitivity, the photosensitive plate is irradiated with light corresponding to an electrical signal to create an electrostatic latent image, and the latent image is developed with toner. The toner image is transferred to a recording medium (hereinafter simply referred to as a sheet), and the transferred toner image is fixed by a fixing device. This fixing device is roughly classified into a heating type and a pressure type, and the heating type includes a heat roller type, an oven type, and a radiation type represented by a flash type.

(3) Problems with the conventional technology In these fixing devices, there is an excessive supply of toner in the developing section, fluctuations in heating temperature in the heating type, and uneven pressure force due to uneven sheet thickness in the pressure type, etc. Poor fixing occurs from time to time.

In addition, the toners used in these products have different characteristics, so the brand of toner to be used is specified depending on the model, and if a different toner is used, normal fixing may not occur. It's normal. However, in recent years, devices that use toner, such as not only printers but also copying machines and fax machines, have become rapidly popular, and the possibility of poor fixing due to the use of unspecified toner has greatly increased.

(4) Purpose of the Invention The present invention has been made in order to deal with such circumstances, and its purpose is to provide a heating type fixing device that can immediately and reliably detect fixing defects. .

(5) Structure of the Invention In other words, in the present invention, a mark is provided on the margin of the print sheet for monitoring the fixing status, the density difference of this mark before and after fixing is measured, and this is compared with a specific value. By doing so, defective fixing can be detected.

Here, a specific example in the case of a radiation type fixing device will be shown as an example.

FIG. 1 shows the relationship between the amount of heat used to fix the toner image and the density of the toner image, where the horizontal axis Q represents the amount of heat absorbed by the toner image per unit area, and the vertical axis D represents the density of the toner image. As the amount of heat absorbed by the toner image increases, the toner starts to melt from the surface,
Adjacent unmelted toner is attracted by the surface tension of the molten toner, so that the sheet is partially exposed, and the density temporarily decreases to d ₁ . When the amount of absorbed heat increases further, the toner is melted over the entire surface, and then the toner in the lower layer that is in contact with the sheet is also melted and begins to penetrate into the sheet, and the density of the toner image reaches the maximum value _d2 . .

If the toner image density, that is, the printing density, is divided into four stages from d ₁ to d ₂ and the adhesion force of the toner to the sheet is observed, the results are approximately as follows.
is a stage where a portion of the surface layer of the toner is melted and a portion of the sheet is exposed, and therefore the toner has almost no adhesion to the sheet and is therefore easily peeled off. In this case, only the surface layer of the toner was melted, but not all of the lower layers were melted, so the adhesion was weak and it was easy to peel off due to friction. In this case, even the toner in the lower layer in contact with the sheet is melted,
Since a portion of the toner penetrates into the sheet, a relatively strong adhesion force is generated between the sheet and the toner, making it difficult for the toner to be easily peeled off due to friction. When this occurs, the toner penetrates the entire surface of the sheet, so at least the penetrated toner cannot be removed by friction.

That is, as the heating progresses and the printing density increases, the adhesion of the toner to the sheet becomes stronger. The present invention utilizes this relationship to compare the print densities of marks provided in advance on the sheet before and after heat fixing, and determines that the density difference is good if it is higher than a predetermined standard print density difference, and if it is lower than is determined to be defective in fixing.

(6) Embodiment of the Invention Fig. 1 shows a system block diagram of an embodiment of the present invention, in which numeral 1 is provided on the outlet side of the heater described later, has a built-in light emitting part and a light receiving part, and emits light from the light emitting part. The light reflected from the sheet S is measured, and the light reflected from the sheet S is measured.
A first photo sensor detects the density of a print density detection mark provided on the sheet S, a heater 2 heats the toner image on the sheet S by radiant heat, and a heater 3 is provided on the inlet side of the heater 2. , a second photo sensor that detects the density of the print density detection mark after heating and fixing on the sheet S; 4 is a first detection circuit that measures the output of the first photo sensor 1; 5 is a second photo sensor; A second detection circuit 6 that measures the output of the photo sensor 3 stores the standard print density difference in advance, calculates the difference between the output of the first detection circuit 4 and the output of the second detection circuit 5, and calculates the difference between the output of the first detection circuit 4 and the output of the second detection circuit 5. This is a comparison circuit that compares the difference in print density with the standard print density difference and generates an alarm signal if the standard print density is not reached.

In the above configuration, the value of the standard print density difference stored in the comparator circuit 6 in advance is set based on the value approximately at the center of the level described in FIG. 1 above. Further, as illustrated in FIG. 3, the density detection mark M is provided outside the printing range (indicated by a chain line) of the sheet S.

In the above embodiment, the density of the toner image before fixing and after fixing was measured at the inlet and outlet sides of the heater 2, respectively, but it is not necessarily necessary to measure the density of the toner image before fixing. do not have.

Further, a printing density detection mark scraping mechanism whose main component is a rotating brush etc. is provided after the heater 2, and the printing density of the printing density detection mark after passing through the scraping mechanism is measured by a second photo sensor 3. The effects of the present invention can be further enhanced by measuring the temperature.

(7) Effects of the Invention As described above, according to the present invention, it is possible to obtain a heating type fixing device that can immediately and reliably detect fixing defects and prevent fixing defects from occurring again.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of heat absorbed by a toner image and the density of the toner image, and FIG. 2 is a configuration diagram of an embodiment of the present invention, in which 1 is a first photosensor, 2 is a heater,
3 is a second photo sensor, and 6 is a comparison circuit.
Further, FIG. 3 shows the placement position of the print density detection mark on the sheet.

Claims (1)

[Claims] 1. In a heating type fixing device that heats and fixes a toner image transferred onto a recording medium, the fixing density of the mark formed on the recording medium after passing through the heater, and the fixing density before passing through the heating device. 1. A heating type fixing device, comprising means for detecting fixing failure by comparing the difference in density with a predetermined density difference.