JP2000122412A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can be equipped with two developing means without increasing the cost thereof. SOLUTION: This image forming device is constituted so that two developing means 4 and 6 for developing an electrostatic latent image on the drum 1 by powder toner can be loaded at the circumference of one rotating photoreceptor drum (electrostatic latent image carrying means) 1. The first developing means 4 out of two developing means 4 and 6 is loaded at the upstream side of the drum 1 in the rotating direction and the second developing means 6 is loaded at the downstream side of the drum 1 in the rotating direction. Besides, developing containers 40 and 60 are provided with aperture parts where the developing rollers (developing electrodes) 41 and 61 of the developing means 4 and 6 are disposed. Then, the whole shape of the rollers 41 and 61 is identical to that of at least the aperture parts of the containers 40 and 60 and the part thereof with which the toner is always brought into contact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, an image recording apparatus, a printer, a facsimile and the like using a powder toner.

[0002]

2. Description of the Related Art Conventionally, computer, facsimile, C
As an image forming apparatus used for a terminal device such as an information device such as an AD or a communication device, an electrostatic recording method using an electrophotographic method or an electrostatic printing method is often used.

In an electrophotographic apparatus, for example, an electrostatic latent image is formed on a pre-charged photoreceptor by a laser beam or the like, and the electrostatic latent image is developed by a developing means to become a visible image. It is usually configured to form a desired image through an image forming process step of transferring a visual image to a transfer material and fixing the transferred visible image to the transfer material, and is generally finally obtained. The recording image on the transfer material is a single black color.

In the case of using a general copy or a printed hard copy, for example, a format and a calculated value or a data value are expressed in different colors, or a part of a drawing output by CAD is replaced with another color. Distinguishing an image in two colors, such as expressing it in two colors, clarifies the printed matter,
Since it is a powerful means in terms of facilitating understanding and further promoting accurate understanding of information, there is a growing demand for enabling multi-color output of at least two colors from the viewpoint of practical document handling. ing.

One of the so-called full-color image forming apparatuses which meets such demands is a so-called full-color image forming apparatus. , A two-color image forming apparatus).

In such a two-color image forming apparatus,
In order to realize color output, two developing means are required. For example, two developing means, a black developing means and a desired color developing means, which are usually used most frequently, are required.

In a two-color image forming apparatus,
Only a user who intends to perform two-color copying does not always use this. For example, a user who needs only a single black color may use this.

[0008] Even when only a single black color is required, there are many users who want to select and output different gloss. Hereinafter, the term “two-color image” includes images of two types of black toner having different gloss.

Here, a method of forming a two-color image will be described with reference to an image forming apparatus shown in FIG.

In FIG. 12, the surface of a photosensitive drum (photoreceptor) 1, which is a latent image forming medium, is uniformly and uniformly charged by a primary charging means 2, and then a first exposure E1 is carried out.
A first latent image is formed thereon, and the first latent image is
The first toner image is developed as a first toner image by using the first color toner t 1, and the first toner image is transferred to the transfer material M by the transfer unit 8. Then, the transfer material M is again conveyed to the transfer unit TZ so as to transfer the second toner image via a transfer material conveyance path (not shown).

Thereafter, the surface of the photosensitive drum 1 is uniformly and again charged by the primary charging means 2, and then the second exposure E2 is performed.
To form a second latent image on the photosensitive drum 1,
The latent image is developed by the second developing means 6 using a second toner t2 of a color different from the first color toner t1 to be visualized as a second toner image, and the second toner image is formed into a first toner image. The toner image is transferred to the transfer material M carrying the toner image, and a two-color image is formed on the transfer material M.

In the above-described two-color image forming method, since the photosensitive drum 1 needs to rotate at least two times, it takes a long time, and when the transfer accuracy of the transfer material M is low, the image of the first color and A shift occurs between the images of the second color, and the first
Since the color and the second color cannot be mixed, there is a problem that the number of representable colors is limited.

A method of forming a two-color image devised to solve the above problem will be described with reference to FIG.

According to the method, the surface of a photosensitive drum (photoreceptor) as a latent image forming medium is uniformly and uniformly charged by a primary charging means (FIG. 13A), and a first exposure E1 is performed to perform the first exposure E1. A first latent image is formed thereon (FIG. 13 (b)), and the first latent image is developed by first developing means using a first color toner t1 (FIG. 13 (c)). The surface of the photosensitive drum is uniformly and again charged by the primary charging means (see FIG. 1).
3 (d)), a second exposure E2 is performed to form a second latent image on the photosensitive drum (FIG. 13 (e)), and the second latent image is formed on the photosensitive drum by the second developing means. Developing using a second toner t2 of a color different from t1 (FIG. 13 (f)),
This is a method of forming a two-color image on a photosensitive drum using two-color toner. In FIG. 13, Vd1 is the photoconductor potential after the first primary charging, Vd2 is the photoconductor potential after the second primary charging,
Vl1 is the photoconductor potential after the first exposure, and Vl2 is the photoconductor potential after the second exposure.

Incidentally, in this method, the same color toner may be used in the two developing steps. For example, when the color is black, the toner is developed with glossy toner in the photographic image area and glossy in the character area, for example, by using toner having the same color but different gloss. By developing the toner with no toner, it is possible to provide a sharp image.

Further, toner having exactly the same gloss as the color may be used. In this case, it is possible to stably provide a high-density image over a long period of time by using two developing units.

[0017]

However, the conventional image forming apparatus described above has a new problem as described below.

That is, since the cost for individually designing the two developing means and the cost for assembling are increased, a considerable increase in price is avoided as compared with an image forming apparatus having only one developing means. The problem is that it cannot be done.

The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus in which two developing units can be provided without increasing the cost.

[0020]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: a rotating electrostatic latent image carrying means; In an image forming apparatus to which two developing means for developing an image with a powder toner can be mounted, a first developing means of the two developing means mounted upstream of a direction of rotation of an electrostatic latent image carrier means. And a second developing means mounted downstream of the electrostatic latent image holding means in the rotational direction, the entire shape of the developing electrodes of these developing means, and a developing container having an opening for disposing the developing electrodes. Among these, at least the opening and the portion that is always in contact with the toner have the same shape.

According to a second aspect of the present invention, in the first aspect of the invention, the color of the toner contained in the first developing means is different from the color of the toner contained in the second developing means. It is characterized by.

According to a third aspect of the present invention, in the invention according to the second aspect, the color of the toner contained in the first developing means is a chromatic color, and the color of the toner contained in the second developing means is The color is black.

According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, the toner contained in the first developing means is a non-magnetic toner and is contained in the second developing means. The toner is a magnetic toner.

According to a fifth aspect of the present invention, in the first to third or fourth aspects of the present invention, the shape of the magnetic field generating means disposed inside the hollow developing electrode and a magnetic substance near the magnetic field generating means are provided. It is characterized in that the magnetic flux density distributions when they do not exist are the same.

According to a sixth aspect of the present invention, in the first to fourth or fifth aspects of the present invention, a two-color image is formed on the electrostatic latent image holding means within a period in which the electrostatic latent image holding means makes one rotation. It can be formed.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a schematic configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view of a developing unit installed in the image forming apparatus, and FIG. Perspective view of a developing roller as a developing electrode installed in the developing means,
FIG. 4 is a partial cross-sectional view showing the configuration of the sleeve of the developing roller.

The image forming apparatus shown in FIG.
A first primary charging means 2 and a first exposure E1 are provided around a photosensitive drum 1 having a diameter of 108 mm and rotating in the direction of arrow A at a peripheral speed of s.
Exposure means 3, first developing means 4, second primary charging means 5, second developing means 6, and second exposure means E2 for applying second exposure E2.
It is provided with exposure means 7 and the like.

In the present embodiment, the surface potential Vd1 of the photosensitive drum 1 after the first charging is -600 V, the surface potential Vl1 of the photosensitive drum 1 after the first exposure (highest intensity) is -150 V, and the surface potential Vd1 after the second charging is The surface potential Vd2 of the photosensitive drum 1 is -700V,
Surface potential Vl2 of photosensitive drum 1 after second exposure (highest intensity)
Is -250V.

Although the first toner and the second toner are the same in that they are black magnetic toners, they have different glosses. For example, a photographic image portion is developed with a glossy toner, and a character portion is a matte toner. , It is possible to provide a sharp image.

After the black toner image formed on the photosensitive drum 1 is collectively transferred onto the transfer material M by the transfer / separation means 8, the transfer material M is sent to the fixing means 9 to fix the toner image. Receiving a black print.

As the photosensitive drum 1, a photosensitive drum provided with a photosensitive layer on a conductive support made of an aluminum alloy can be used. The photosensitive layer has a laminated structure of a charge generation layer containing a charge generation material dispersed in a binder resin and a charge transport layer containing a charge transport material. In this case, the charge transport layer is laminated on the charge generation layer.
The photosensitive drum 1 may have a conductive polymer layer or a resin layer containing conductive particles such as tin oxide, titanium oxide, and silver particles as necessary. Further, an undercoat layer (adhesive layer) having a barrier function and an undercoat function can be provided between the conductive support and the photosensitive layer.

The polycarbonate resin was used as a binder resin for forming the charge transport layer. You may choose from.

The charge generation layer or the charge transport layer may contain various additives such as an antioxidant, an ultraviolet absorber and a lubricant. Further, a protective layer can be further applied on the photosensitive layer.

As shown in FIG. 2, the first developing means 4 is
A developing container 40 made of resin containing a one-component magnetic powder toner as the toner t1 is provided. An opening 40c of the developing container 40 facing the photosensitive drum 1 has a developing roller 41.
Is provided. The developing roller 41 carries the toner t1 on its surface, and is rotationally driven in the direction of arrow Q at a peripheral speed of 490 mm / s by a motor via a gear, clutch or the like (not shown).

The developing roller 41 as a developing electrode is shown in FIG.
As shown in FIG. 7, a developing sleeve 41a having a hollow cylindrical shape (outer diameter of 24.5 mm), a roller-like magnet 41b (see FIG. 2) fixed and disposed inside the developing sleeve 41a, and both ends of the developing sleeve 41a are coupled to each other. It is composed of stainless steel flanges 41c, 41d and the like supported by the container 40, and a predetermined gap _GSD1 is formed between the photosensitive drum 1 and the photosensitive drum 1 (see FIG. 2). The gap G _SD1 is 200 to 220
μm is preferred.

The developing sleeve 41a is disposed with a predetermined gap G _SB1 between the developing sleeve 41a and a toner regulating blade 43 made of magnetic steel as a toner layer forming means. The gap G
_SB1 is preferably 180 to 240 μm.

In the developing sleeve 41a, as shown in FIG. 4, the base layer 41a1 is made of an aluminum alloy, and after its surface is subjected to a surface roughening treatment by spraying glass fine particles, a phenol resin and a crystalline A low electric resistance coating 41a2 containing graphite, carbon or the like as a component is provided.

The roller-shaped magnet 41b has six magnetic poles, including an N2 pole near the developing section, an N1 pole near the toner regulating blade 43, and an S1 pole between the N2 pole and the N1 pole. A normal magnetic flux density Br distribution as shown in FIG.

A developing bias having a waveform as shown in FIG. 6 in which an AC voltage is superimposed on a DC voltage is applied to the gap between the developing sleeve 41a and the photosensitive drum 1, and the electrostatic latent image on the photosensitive drum 1 is developed. You.

The amplitude Vpp of the first developing bias is 1200
V, frequency f (= 1 / T) is 2000 Hz, average voltage V
m is -450V.

Since the second developing means 6 has substantially the same structure as the first developing means 4, its detailed description is omitted. However, the second image means 6 is provided in the developing container 60 with an opening for accommodating the developing roller 61 and a portion where the toner is always present (a portion below the toner existing area immediately after the toner replenishing operation by the toner replenishing means is completed). 2 (in FIG. 2, the broken line indicates the developing container 40 of the first developing unit 4).
Is the same as the shape of the developing container 40 of the first developing means 4 (see FIG. 2).

As shown in FIG. 10, upper portions 40a, 6a of developing containers 40, 60 of first developing means 4 and second developing means 6 are provided.
Reference numeral 0a is coupled to the shared developing container lower portions 40b and 60b by means such as a screw or an adhesive. The reason why the height of the second developing means 6 is lower than that of the first developing means 4 is to secure an arrangement space for the second primary charging means 5 and the like and an optical path of the second image exposure E2. The shapes of the developing rollers 41 and 61 and the arrangement of the magnetic poles of the magnets 41b and 61b are naturally common.

The magnets 41b and 61b are fixed by a metal fixing plate (not shown). However, the magnets 41b and 61b are the same (length: 304 mm, outer diameter: 22.3 mm) and are moved from each other in the circumferential fixing position. (See FIG. 2).

Further, the toner regulating blades 43 and 63 and a part of the toner stirring means 44 and 64 and 45 and 65 are also shared.

The one-component magnetic powder toner as the second toner t2 has the same weight average particle diameter as the first toner t1 of 8 μm.
Although it is mainly composed of polyester, there are some differences due to different gloss. The details of the difference are omitted.

The charge amount of the toner on the developing sleeves 41a and 61a is 8 to 10 μC / g in a normal temperature and normal humidity environment. The developing bias for the second developing is such that the average voltage Vm is -550.
Except for V, it is the same as the first development.

As shown in FIG. 2, a predetermined gap G _SD2 is formed between the developing roller 61 and the photosensitive drum 1, and the gap G _SD2 is set to 200 to 220 μm.

Designed by the conventional design method, that is,
Assuming that the cost of the image forming apparatus having no part common to the components of the first developing means and the second developing means is 1, the cost of the image forming apparatus according to the present embodiment is about 0.88.

<Embodiment 2> Next, an image forming apparatus according to Embodiment 2 of the present invention will be described, but the description of the same parts as those in the above-described embodiment will be omitted.

FIG. 7 is a sectional view of the developing means provided in the image forming apparatus according to the present embodiment.

In the developing means according to the present embodiment, the first
In the development, a two-component developer containing magnetic carrier particles containing Mn-Zn ferrite as a main component and a non-magnetic toner t1 containing polyester as a main component is used.

The non-magnetic toner t1 has a red color on the print, to which 3 parts by weight of hydrophobically treated silica has been added as an external additive. The weight average particle diameter of the toner t1 is 9.
5 μm, which is larger than the particle diameter of the second toner t2, 8 μm. As described above, the weight average particle diameter of the first toner t1 is changed to the second toner t1.
By making the toner t2 larger than that of the toner t2, when the first toner t1 is mixed into the second developing unit 6, the first toner t1
This is because it has been found that the effect of naturally discharging 1 from the second developing means 6 can be obtained.

First toner t1 on developing sleeve 41a
Has an average charge amount of −20 to 25 μC / g in a normal temperature and normal humidity environment.

The average concentration of the toner in the developer is 7 to 8% by weight. The average toner density is detected and controlled by a density detector (not shown) embedded in the developer flow control member 48, but the detailed description thereof is omitted.

The shapes (length and outer diameter) of the developing roller 41 and the magnet 41b of the first developing means 4 are the same as those of the developing roller 61 and the magnet 61b of the second developing means 6.

However, the developing sleeve 4 of the first developing means 4
The material of 1a is stainless steel (SUS305),
No coating after surface roughening treatment by spraying fine particles made of alumina.

Further, the arrangement of the magnetic poles of the magnet 41b and the magnetic flux density are different from those in the first embodiment. This is mainly due to the fact that the configurations of the developer of the first development and the developer of the second development are greatly different.

In the two-component developing method, a necessary charge is given to the toner particles by the contact between the carrier particles and the toner particles. The developer agitation transport members 46 and 47 are disposed, and the emphasis is placed on transporting the developer while agitating the developer from the front to the back of the developing means 4 and from the back to the front. Here, an additional partition 49 is provided to prevent the developer transported from the front to the back from mixing with the developer transported from the back to the front.

The developer regulating blade 43 of the first developing means 4
Is made of non-magnetic steel and the gap G _SB1 is 350 to 4
20 μm is desirable.

The second developing means 6 is pressed against the photosensitive drum 1, and a dedicated bias is applied to the developing sleeve 61a. That is, as a countermeasure against mixing of the first toner t1 into the second developing means 6, as shown in FIG. 8, a potential difference for moving the toner t1 from the photosensitive drum 1 to the developing sleeve 61a side with respect to the AC component of the second developing bias. V1 has a waveform smaller than the potential difference V2 for moving the toner t1 to the photosensitive drum 1 side. Note that η (= V2 / (V1 + V
2): The duty ratio is preferably about 0.2 to 0.4.

As the developing conditions, the gap G _SD2 = 300 μm
m, amplitude Vpp of developing bias = 1300 V, frequency f
(= 1 / T) = 1800 Hz, duty ratio η = 0.3
Is set to

In the image forming apparatus according to the present embodiment, in addition to the two-color mode, which is the normal mode, if the user desires, a black single-color mode in which only the black developing step is performed or a single-color mode in which only the color developing step is performed is set. Can be selected.

In the multi-color black mode, the first developing means 4 is separated from the photosensitive drum 1 in the single-color mode, so that unnecessary toner is prevented from adhering.

A fan 151 and a duct 152 are provided as a device for sucking floating toner from the developing means 4 and 6. The duct 152 has a suction part 152a disposed in the direction of the developing part of the image forming part, is integrally formed up to the back side of the two-color image forming apparatus, and has a filter 153 for toner repair disposed in the discharge part 152b. (See FIG. 7).

FIG. 11 shows the developing means 4 according to the present embodiment.
6 is a perspective view of a common portion 40b, 60b of a sixth developing container 40, 60. FIG.

Designed by the conventional design method, that is,
Assuming that the cost of the image forming apparatus having no part common to the components of the first developing means and the second developing means is 1, the cost of the image forming apparatus according to the present embodiment is about 0.91.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 9 is a sectional view of the developing means according to the present embodiment. In this embodiment, the description of the same items as in the second embodiment will be omitted.

The difference between the present embodiment and the second embodiment is that the first developer is a one-component developer composed of only a non-magnetic toner.

By using such a developer, the frequency of replacement of the developing means is increased, but the developing means is simplified and the cost is reduced.

That is, although the toner concentration detecting means and the screw-shaped developer stirring and conveying member in the first developing means of the image forming apparatus according to Embodiment 2 are both expensive,
Inexpensive toner remaining amount detecting means and a resin blade-like stirring member 45 are sufficient.

Further, the non-magnetic toner t1 is applied to the developing sleeve 4
A magnet is not required inside the developing sleeve 41a because no magnetic force can be applied when the toner is applied to the coating 1a, but an elastic roller 49 is required as a means for mechanically applying the toner. Further, as the toner layer type means, an elastic blade 43 in contact with the developing sleeve 41a is used.

The charge amount of the first toner t1 on the developing sleeve 41a is -20 to -25 .mu.C / g in a normal temperature and normal humidity environment.

Designed by the conventional design method, that is,
Assuming that the cost of the image forming apparatus having no part common to the components of the first developing means and the second developing means is 1, the cost of the image forming apparatus according to the present embodiment is about 0.82.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.

Except for the matters described below, the configuration is the same as that of the second embodiment.

That is, the second developer (black toner) in the second embodiment is used as the first developer in the present embodiment, and the first developer (red toner) in the second embodiment is used in the present embodiment. Was used as a second developer.

Regarding the developing conditions, the second developing condition in the first embodiment is used as the first developing condition in the present embodiment, and the second developing condition in the first embodiment is used in the present embodiment. It was used as a condition for the first development.

According to the image forming apparatus of this embodiment, although the level of color mixture is slightly deteriorated, the means for increasing the toner charge after the second development is unnecessary.

Designed by the conventional design method, that is,
Assuming that the cost of the image forming apparatus having no part common to the components of the first developing means and the second developing means is 1, the cost of the image forming apparatus according to the present embodiment is about 0.80.

Table 1 summarizes the performance evaluations in the first to fourth embodiments described above.

[0083] Although various examples have been described above, the present invention is not limited to the configurations described in these embodiments, and various changes and substitutions within the scope of the present invention are possible. Needless to say.

That is, two or more developing rollers may be provided for one developing means, or may be constituted by an elastic body or the like and contact the photosensitive member.

As for the shape of the developing electrode, a belt-shaped one can be used in addition to a roller-shaped one. The developer layer forming means is not limited to the plate-shaped one, but may be a columnar one, and may be further driven to rotate. Further, the developing container may be made of a non-magnetic metal material such as an aluminum alloy.

[0086]

As is apparent from the above description, according to the present invention, the electrostatic latent image on the electrostatic latent image holding means is powdered around one rotating electrostatic latent image holding means. In an image forming apparatus to which two developing means for developing with toner can be mounted, a first developing means and an electrostatic latent image which are mounted in the rotation direction upstream of the electrostatic latent image carrier means among the two developing means. The second developing means mounted downstream in the rotation direction of the image bearing means has at least the shape of the developing electrodes of these developing means and at least the opening of a developing container provided with an opening for disposing the developing electrode. Since the portion and the portion that the toner always contacts have the same shape, the effect that two developing units can be provided without increasing the cost is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view of a developing unit of the image forming apparatus according to the present invention.

FIG. 3 is a perspective view of a developing roller as a developing electrode provided in a developing unit of the image forming apparatus according to the present invention.

FIG. 4 is a partial cross-sectional view showing a configuration near the surface of a developing sleeve of the developing roller.

FIG. 5 is a diagram showing a magnetic flux density distribution of a magnet which is a magnetic field generating means of the developing roller.

FIG. 6 is a diagram showing a developing bias waveform.

FIG. 7 is a sectional view of a developing unit of the image forming apparatus according to the present invention.

FIG. 8 is a diagram showing a developing bias waveform.

FIG. 9 is a sectional view of a developing unit of the image forming apparatus according to the present invention.

FIG. 10 is a perspective view showing a common portion of a developing container of a developing unit of the image forming apparatus according to the present invention.

FIG. 11 is a perspective view showing a common portion of a developing container of a developing unit of the image forming apparatus according to the present invention.

FIG. 12 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 13 is a diagram illustrating a transition of a photoconductor potential for describing a two-color image forming method.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (electrostatic latent image holding means) 4 first developing means 6 second developing means 40, 60 developing container 41, 61 developing roller (developing electrode) 41a, 61a developing sleeve 41b, 61b magnet (magnetic field generating means) ) T1, t2 Toner

Claims (6)

[Claims] An image capable of mounting two developing units for developing an electrostatic latent image on the electrostatic latent image holding unit with powder toner around one rotating electrostatic latent image holding unit. In the forming apparatus, of the two developing units, a first developing unit mounted upstream in the rotation direction of the electrostatic latent image carrier unit and a second developing unit mounted downstream in the rotation direction of the electrostatic latent image holding unit The means is that the entire shape of the developing electrodes of these developing means is the same as the shape of at least the opening and the portion of the developing container provided with the opening where the developing electrode is always in contact with the toner. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the color of the toner stored in the first developing unit is different from the color of the toner stored in the second developing unit. 3. The toner according to claim 2, wherein the color of the toner stored in the first developing unit is a chromatic color, and the color of the toner stored in the second developing unit is black. Image forming apparatus. 4. The toner according to claim 1, wherein the toner contained in the first developing means is a non-magnetic toner, and the toner contained in the second developing means is a magnetic toner. 3. The image forming apparatus according to 3. 5. The magnetic field generating means provided inside the hollow developing electrode has the same shape as the magnetic field density distribution when no magnetic substance is present near the magnetic field generating means. An image forming apparatus according to any one of claims 1 to 3. 6. The image forming apparatus according to claim 1, wherein a two-color image can be formed on the electrostatic latent image holding unit within a period in which the electrostatic latent image holding unit makes one rotation. Image forming device.