The present application is based on and claims priority from Japanese Patent Application No. 2011-160352, filed on Jul. 21, 2011, the disclosure of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a photosensor to emit light to a target object and receive light reflected thereby as well as to an image forming device such as a copier, a printer or a facsimile machine incorporating such a photosensor.
2. Description of the Related Art
Some image forming device having a photosensor generates a toner patch as a referential pattern on the surface of an image carrier and detects the density of the toner patch for the purpose of realizing stable image density. To control image density, such an image forming device adjusts develop potential by changing charge bias, developing bias, and light intensity for forming an electric latent image or adjusts a target toner density of two-component developer in a develop unit on the basis of a detected result of the photosensor. This type of photosensor is generally a reflective photosensor having a light emitting element and a light receiving element.
Japanese Patent Application Publication No. 2008-261864 discloses a photosensor including light emitting and light receiving elements of a surface mount type on a printed circuit board. There are two types of light emitting element, a top view surface mount type to emit light to a printed circuit board orthogonally, and a side view surface mount type to emit light thereto in parallel. Likewise, a top view surface mount type light receiving element receives light orthogonally relative to the printed circuit board while a side view surface mount type light receiving element receives light in parallel to the printed circuit board. The same type of light emitting element and light receiving element are used together.
These light emitting element and light receiving element (hereinafter, referred to as simply element when appropriate) are each provided with L-shaped output terminal and input terminal composed of one portion extending to the printed circuit board and the other portion continuing from the end of the one portion and extending in parallel to the printed circuit board. To mount each of the elements on the surface of the printed circuit board, the other parallel portions of the terminals and the connecting portions of the printed circuit board are joined by soldering.
In fixing the element on the printed circuit board by soldering, only the pair of input and output terminals is placed thereon. That is, the element is supported by the two terminals only when mounted. This may cause a problem that the element is mounted in an unintended posture on the circuit board. For example, such a problem occurs when the extending portion and the parallel portion of the terminal make an angle other than a preset angle of 90 degrees due to a processing error. Further, there is a gap between the circuit board and the opposing surface of the element so that the element supported by the two terminals may be swayed about the terminals as fulcrum in the gap. Because of this, while melted solder between the connecting portions of the circuit board and the terminals is being hardened, the elements may be touched and swayed to partially contact the printed circuit board, and fixed thereto in an inclined posture.
The present invention aims to provide a photosensor including a light emitting element and a light receiving element properly mounted in a certain posture on a circuit board as well as an image forming device incorporating such a photosensor.
According to one aspect of the present invention, a photosensor includes a light emitting element to emit light to a target object, a light receiving element to receive the light emitted from the light emitting element and reflected by the target object, and a circuit board on which the light emitting element and the light receiving element are mounted, including at least one protrusion thereon, in which the light emitting element and the light receiving element each have a terminal; and the at least one protrusion is configured to support one of the light emitting element and the light receiving element in a contact manner in a state that the terminal is electrically connected to the circuit board.
Features, embodiments, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings:
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
A full color printer 100 (hereinafter, simply printer) as an example of the image forming device according to the present embodiment is described.
The charge rollers 3Y, 3C, 3M, 3K uniformly charge the photoreceptor drums 2Y, 2C, 2M, 2K with the same polarity (negative in the present embodiment) as that of toner with a predetermined electric potential. Alternatively, various types of charge elements such as a charge brush can be arbitrarily used instead of a charge roller.
The laser exposure unit 20 exposes portions of the photoreceptor drums 2Y, 2C, 2M, 2K between the charge rollers and the develop units. It is disposed in parallel to the rotary axes of the photoreceptor drums 2Y, 2C, 2M, 2K to expose them in main scan direction.
The laser exposure unit 20 includes, for example, a semiconductor laser (LD) as a light source, a coupling system or beam adjusting system made up of a collimate lens or a cylindrical lens, an optical deflector as a polygon mirror, and an imaging system to converge laser beams deflected by the optical deflector on the photoreceptor drums 2. It exposes the surfaces of the photoreceptor drums 2Y, 2C, 2M, 2K with laser beams Ly, Lc, LM, LK at different intensity on the basis of image data stored in a memory or input from an external device as a PC, to form electrostatic latent images of the four colors thereon. Alternatively, the laser exposure unit 20 can be an LED write unit comprised of an LED array and a lens array.
The bodies of the photoreceptor drums 2Y, 2C, 2M, 2K are each layered with an underlying layer, a charge generating layer, and a charge carrying layer in this order or a reverse order. A known surface protective layer or overcoat layer made from thermoplastic or thermosetting polymer can be additionally layered on the charge generating layer or charge carrying layer, for example. In the present embodiment the bodies of the photoreceptor drums 2Y, 2C, 2M, 2K are grounded.
The develop units 4Y, 4C, 4M, 4K include develop sleeves 41Y, 41C, 41M, 41K made from non-magnetic stainless steel or aluminum which are arranged with a predetermined interval relative to the circumferences of the photoreceptor drums 2 to rotate in the rotary direction of the photoreceptor drums 2. They contain four color one-component or two-component developers. In the present embodiment the develop units 4 contain two-component developer of toner (negative-charged) and magnetic carrier, and magnet rolls with fixed magnets or magnetic poles are provided in the develop sleeves 41. The develop units 4Y, 4C, 4M, 4K further comprise agitation elements 42, supply portions 43 to supply toner from four-color toner bottles 22, and density sensors 44Y, 44C, 44M, 44K to detect the density of toner in the developer when needed.
The develop sleeves 41Y, 41C, 41M, 41K are held by not-shown rollers with a predetermined interval, 100 to 500 μm for example relative to the photoreceptor drums 2Y, 2C, 2M, 2K so as not to contact the surfaces thereof. The develop sleeves are then applied with developing bias of superimposed direct and alternate current voltages to inversely develop the electrostatic latent images on the surfaces of the photoreceptor drums 2Y, 2C, 2M, 2K in contact or non-contact manner and form toner images thereon.
The cleaning units 6Y, 6C, 6M, 6K include cleaning blades 61 contacting the photoreceptors' surfaces and cleaning rollers 62 or brushes, for example.
The intermediate transfer belt 7 as an image carrier is extended over a drive roller 8 doubling as a secondary transfer backup roller, a support roller 9, tension rollers 10a, 10b, and a backup roller 11 and rotates counterclockwise as indicated by the arrow in
The primary transfer rollers 5Y, 5C, 5M, 5K form transfer areas between the photoreceptor drums 2Y, 2C, 2M, 2K and the intermediate transfer belt 7. Applied with direct current voltage of positive polarity (reverse to the polarity of toner) by a not-shown power source, the primary transfer rollers 5Y, 5C, 5M, 5K form magnetic fields in the transfer areas to transfer the toner images on the photoreceptor drums 2Y, 2C, 2M, 2K to the intermediate transfer belt 7.
The secondary transfer roller 14 opposes the grounded drive roller 8 over the intermediate transfer belt 7 and is applied with direct current voltage of positive polarity to transfer a superimposed toner image on the intermediate transfer belt 7 to a paper sheet S.
The paper sheet S is carried by the feed roller 27 from the paper cassette 21 through a resist roller pair 13 to the intermediate transfer belt 7 held between the secondary transfer roller 14 and the drive roller 8. The toner image is transferred onto the paper sheet S from the intermediate transfer belt 7 in a secondary transfer unit, and then the paper sheet S is carried to a fuser unit 15 to fuse the image by thermal welding of a fuse roller 15a and a pressure roller 15b, and discharged to a discharge unit 18.
The printer according to the present embodiment includes a controller configured to properly adjust the density of four color images upon power-on or after feeding through a certain number of paper sheets. In image density control the charge bias and developing bias are switched when appropriate to create four-color tone patterns Sy, Sc, Sm, Sk as toner image for density adjustment on the intermediate transfer belt 7, as shown in
A photosensor unit 300 in
The side view surface mount type light emitting and receiving elements 31 to 33 have the same structure so that only the light emitting element 31 is described in the following.
Due to the crown-shaped body 312 of the light emitting element 31, when the output and input terminals 313a, 313b are placed on the connecting portions 34d, a very small gap of several dozen gm occurs between the front (lens side) and rear ends of the body 312 and the printed circuit board 34 as shown in
As shown in
In view of the above, according to the present embodiment the printed circuit board 34 includes protrusions to support the elements 31 to 33.
The protrusions 34e are formed on the printed circuit board 34 by silk screen printing. Specifically, marks indicating the mount positions of electric elements are formed on the resist layer 34c of the printed circuit board 34. The protrusions 34e are formed on the resist layer 34c by silk screen printing concurrently with the marks. Thus, the protrusions 34e can be simply formed.
The height of the protrusions 34e is 20 to 50 μm. Depending on the element's shape or other factors, the height thereof may not reach a desired height enough to support the element by silk screen printing at once. It is preferable to form the protrusions 34e at a desired height by silk screen printing at multiple times as shown in
According to the present embodiment the protrusions 34e can sufficiently support the front and back sides of the bodies of the light emitting and receiving elements and prevent them from swaying about the terminals. This prevents the elements from tilting forward or backward along the optical axis even if the elements are accidentally touched while the melted solder filled in between the connecting portions 34d and the terminals is hardened. Accordingly, the elements are prevented from being mounted askew on the printed circuit board 34. Further, even with the downward extending portion and parallel portion of the terminal not precisely set at the right angle due to a processing error, the protrusions 34e can appropriately support the elements with no inclination on the printed circuit board 34.
Alternatively, for an element with gravity center on the front (lens side), only one protrusion 34e instead of two can be provided on the printed circuit board 34 at a position opposing the front end of the body of the element as shown in
Furthermore, the side view mount type light receiving element may receive ambient light reflected by the surface of the printed circuit board. Especially, the ambient light may affect the first light receiving element 32 to receive specularly reflected light from the target object and cause noise therein, resulting in deteriorating the accuracy at which the amount of specularly reflected light is detected. To prevent this, a shield wall 341 in
Therefore, it is preferable to provide only one protrusion 34e on the printed circuit board 34 to oppose the front end of the body as shown in
Further, not only the first light receiving element 32 but the light emitting element 31 and the second light receiving element 33 can be mounted on the printed circuit board with the back ends of their bodies abut thereon.
Next, an example of a photosensor comprising top view surface mount type light emitting element and light receiving element is described with reference to
The light emitting and receiving elements 31 to 33 have the same structure so that only the light emitting element 31 is described in the following.
The top view surface mount type has the same problem as the side view surface mount type that the element 31 is fixed in an inclined posture on the printed circuit board 34 by soldering if the angles between the downward extending portions and parallel portions of the terminals are not the right angle due to a processing error.
Thus, the photosensor 30A is configured to include two protrusions 34e on the printed circuit board 34 at positions opposing the right and left ends of the bottom surface of the element 31 as shown in
The height of the protrusions 34e is formed to be a predetermined height by silk screen printing at multiple times when it does not reach the height by silk screen printing at once. Further, the linear protrusions 34e can extend in parallel to the parallel portions of the terminals as shown in
Further, the two protrusions 34e can be different in height as shown in
Instead of attaching the element to the printed circuit board and then filling it with the solder, melted solder can be applied to the connecting portions 34d by silk screen printing first and then the element is attached to the printed circuit board, for example. Also, in this case the protrusions can securely support the element in a certain posture on the printed circuit board.
As described above, the photosensor according to any of the above embodiments includes, on the circuit board, one or both of the protrusions to support the light emitting element and/or the light receiving element. By properly forming the shape and height of the protrusions and placing them at the right location, the protrusions can prevent the light emitting and receiving elements from tilting and securely support them in a certain posture on the circuit board, even with the input and output terminals of an unintended shape due to a processing error. Accordingly, compared with the light emitting and receiving elements supported only by the terminals, they can be securely mounted on the circuit board without a change in posture. Moreover, the elements can be prevented from swaying while melted solder filled between the connecting portions and the terminals is hardened.
Further, the image forming device incorporating the above photosensor can properly receive reflected light by a toner image for density adjustment and accurately adjust image density.
Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. It should be appreciated that variations or modifications may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims.
Number | Date | Country | Kind |
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2011-160352 | Jul 2011 | JP | national |