JP4645317B2 - Sheet sensor, sheet conveying apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet sensor that detects a sheet conveyed along a sheet conveying path, a sheet conveying apparatus including the sheet sensor, and an image forming apparatus including the sheet conveying apparatus, and more particularly, along the sheet conveying path. Sheet sensor for detecting sheet detection light including reflected light (sheet reflected light) from conveyed sheet or light transmitted through the sheet (sheet transmitted light), sheet conveying apparatus including the sheet sensor, and sheet conveying apparatus The present invention relates to an image forming apparatus including The sheet sensor of the present invention is preferably used in an image forming apparatus such as a printer, a copying machine, a FAX, or a multifunction machine having a plurality of these functions.

In a conventional image forming apparatus, many sensors such as a sheet position sensor for detecting the position of a sheet and a sheet type sensor for detecting the type of sheet are used. Examples of the sensor include a transmissive sensor that irradiates detection light from a light emitting unit onto a sheet surface and uses light transmitted through the sheet, and a reflective sensor that uses light reflected on the sheet surface.
The sensor may not be able to accurately detect due to the flapping of the sheet. In order to perform accurate detection, it is desirable to perform sensing with a stable posture without flapping of the sheet. For this reason, in many cases, a sensor is arranged in the vicinity of the registration roll that is fed out after the sheet is temporarily stopped, and detection is performed in a state in which the sheet is stopped and influences such as flapping are reduced.
The following prior arts (J01) and (J02) are known as techniques for disposing the sensor near the registration roll.

(J01) Technology described in Patent Document 1 (Japanese Patent Laid-Open No. 2002-347983) Patent Document 1 describes a sheet conveyance path through which a sheet fed from a manual feed tray or an inverted sheet is conveyed, and a sheet feeding path. A technique is described in which a sheet sensor detects a sheet conveyed to a registration roll disposed at a merging point between a sheet conveyance path through which a sheet that has been conveyed is conveyed.
(J02) Technology described in Patent Document 2 (Japanese Patent Laid-Open No. 10-329984) In Patent Document 2, in a sheet conveyance path in which a sheet sensor is arranged, a sheet temporarily stopped at a nip portion of a registration roll is curved (loop formation). Thus, a technique for detecting a sheet by the sheet sensor is described.

(Problems of the technology described in Patent Document 1)
In Patent Document 1, accurate detection cannot be performed because the distance between the sheet and the sheet sensor may vary between the reversed sheet and the sheet fed from the manual feed tray and the sheet fed from the sheet feed tray. There is a fear.
(Problems of the technology described in Patent Document 2)
In Patent Document 2, the size of the loop formed on the sheet may vary in the sheet conveyance path where the sheet sensor is arranged, and the distance between the sheet and the sheet sensor may vary. For this reason, there is a possibility that the sheet sensor cannot perform accurate detection.

In contrast to the prior arts (J01) and (J02) in which the distance between the sheet and the sensor may vary, the following prior art (J03) is known as a technique for performing detection by bringing the sheet into contact with the sensor.
(J03) Technology described in Patent Document 3 (Japanese Patent Laid-Open No. 2003-276902) Patent Document 3 describes that when the front end of a sheet passing through a curved sheet conveyance path reaches a feed roller, the feed roller is driven to rotate reversely. Then, a drive roller disposed upstream of the feed roller in the sheet conveying direction is driven to rotate forward to form a loop in the sheet, and the sheet is placed on a sensing surface of a sheet sensor disposed on the upper side of the sheet conveying path. A technique for detecting the glossiness of the sheet when touched is described.

JP 2002-347983 (paragraph number “0008”, FIGS. 1 and 5) Japanese Patent Laid-Open No. 10-329984 (paragraph number “0081”, FIGS. 2 and 5) JP 2003-276902 A (paragraph numbers “0031” to “0034”, FIG. 1)

FIG. 7 is an explanatory diagram of a conventional sheet sensor.
(Problems of the technology described in Patent Document 3)
7, in the technique described in Patent Document 3, a sheet 03 conveyed between a feed roller 01 and a drive roller 02 is detected by a sensor 06 disposed above a sheet conveying path 04 that is curved upward. The detection signal is not output unless it touches the surface. Therefore, it is necessary to form a sufficiently large loop (see the broken line in FIG. 7) so that the sheet contacts the sensing surface. However, when thin paper is used as the sheet 03, the loop formed as shown by the solid line in FIG. 7 is recessed or bent due to the low rigidity of the thin paper (weakness of the strain) and the action of gravity. The large loop which contacts the sensing surface of the sensor 06 arrange | positioned above the sheet | seat conveyance path 04 curved convexly upwards may become unable to be formed. That is, with the technique described in Patent Document 3, there is a possibility that accurate detection may not be possible depending on the type of sheet.

In view of the above-described circumstances, the present invention has the following description (O01).
(O01) To accurately detect various sheets.

  Next, the present invention for solving the above problems will be described. Elements of the present invention are enclosed in parentheses with reference numerals of the elements of the embodiment in order to facilitate correspondence with elements of the embodiment described later. Add a note. The reason why the present invention is described in correspondence with the reference numerals of the embodiments to be described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(First invention)
In order to solve the above technical problem, the sheet sensor of the first invention is characterized by comprising the following structural requirements (A01), (A02) , and (A02a) .
(A01) The front end of the conveyed sheet (S) is temporarily stopped and the sheet (S) is bent to correct the inclination of the sheet (S), and then the sheet (S) is moved downstream in the sheet conveying direction. It is provided on the upstream side of the registration roll (Rr) that is conveyed to the side, and is disposed on the protruding surface side of the sheet (S) that is conveyed in a curved state along a curved conveying path (SH1b) that is curved so as to protrude downward. Sheet sensor (SN2) ,
(A02) The light detection unit ( 7, 8 ) which detects the sheet detection light irradiated on the sheet (S) temporarily stopped in the curved conveyance path (SH1b) and is supported by the sensor support member ( SN2a ). Sheet sensor ( SN2 ) ,
(A02a) a light emitting unit (6) for irradiating the sheet with the sheet detection light, and the light receiving unit (7, 8) for receiving light from the sheet (S) irradiated with the sheet detection light. Have
Both the light emitting part (6) and the light receiving part (7, 8) are arranged in the lower guide (SG3) that contacts and guides the lower surface of the sheet (S) that curves convexly downward. And
The light emitting part (6) and the light receiving part (7, 8) are arranged along the conveying direction of the sheet (S).
The sheet sensor (SN2).

(Explanation of terms)
The “downward” described in the first invention includes not only “directly downward” but also “obliquely downward”.

(Operation of the first invention)
The sheet sensor ( SN2 ) according to the first aspect of the present invention having the structural requirements (A01), (A02) , (A02a) temporarily stops the front end of the conveyed sheet (S) and curves the sheet (S). Then, after correcting the inclination of the sheet (S), it is provided on the upstream side of the registration roll (Rr) that conveys the sheet (S) to the downstream side in the sheet conveyance direction, and is curved so as to protrude downward. It is arranged on the protruding surface side of the sheet (S) that is conveyed in a curved state along the conveyance path (SH1b).
The sheet sensor ( SN2 ) has a light receiving portion ( 7, 8 ) supported by a sensor support member ( SN2a ). The light receiving section ( 7, 8 ) detects sheet detection light applied to the sheet (S) temporarily stopped in the curved conveyance path (SH1b).
The sheet sensor (SN2) includes a light emitting unit (6) that irradiates the sheet with the sheet detection light, and a light receiving unit (6) that receives light from the sheet (S) irradiated with the sheet detection light. 7, 8). Both the light emitting part (6) and the light receiving part (7, 8) are arranged in the lower guide (SG3) that contacts and guides the lower surface of the sheet (S) that curves convexly downward. Has been. Furthermore, the light emitting part (6) and the light receiving part (7, 8) are arranged along the conveying direction of the sheet (S).

(Embodiment 1 of the first invention)
The sheet sensor according to the first aspect of the first invention is characterized in that, in the first invention, the following structural requirement (A03) is provided.
(A03) Sheet sensors (SN1, SN2) having the light receiving portions (2, 7, 8) facing the sheet (S) and arranged upward.
(Operation of Form 1 of the First Invention)
In the sheet sensor (SN1, SN2) according to the first aspect of the first invention having the structural element (A03), the light receiving part (2, 7, 8) faces the sheet (S) and is arranged upward. Has been.

(Second invention)
In order to solve the technical problem, the sheet conveying device (Ra, Rr, SH1b, SN1, SN2) of the second invention is a sheet sensor (SN1, SN2) of the first invention or the first embodiment of the first invention. It is provided with.
(Operation of the second invention)
The sheet conveying device (Ra, Rr, SH1b, SN1, SN2) of the second invention having the above-described configuration includes the sheet sensor (SN1, SN2) described in the first invention or the first embodiment of the first invention.

(Third invention)
In order to solve the technical problem, an image forming apparatus (U) according to a third aspect of the invention includes the sheet conveying apparatus (Ra, Rr, SH1b, SN1, SN2) according to the second aspect of the invention.
(Operation of the third invention)
The image forming apparatus (U) of the third invention having the above-described configuration includes the sheet conveying device (Ra, Rr, SH1b, SN1, SN2) of the second invention.

The above-described present invention has the following effect (E01).
(E01) Various sheets can be accurately detected.

Next, embodiments (examples) of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The directions indicated by Z and -Z or the indicated side are defined as front, rear, right, left, upper, lower, or front, rear, right, left, upper, and lower, respectively.
In the figure, “•” in “○” means an arrow pointing from the back of the page to the front, and “×” in “○” is the front of the page. It means an arrow pointing from the back to the back.

Example 1
1 is a perspective explanatory view of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is an overall explanatory diagram of the image forming apparatus according to the first exemplary embodiment.
In FIG. 1, a printer U as an image forming apparatus according to a first embodiment of the present invention has a paper feed cassette TR1 in which a sheet on which an image is recorded is accommodated in a lower portion, and a discharge tray TRh is provided on an upper surface. It has been.
In FIG. 2, the printer U includes a controller C constituted by a microcomputer, an IPS (image processing system) whose operation is controlled by the controller C, a laser drive circuit DL, a power supply device E, and the like. The power supply device E applies a bias voltage to charging rollers CRy to CRk, developing units Gy to Gk, a transfer roller Rt, and the like which will be described later.

  The IPS (image processing system) uses print data input from an external host computer or the like as latent images corresponding to four color images of K (black), Y (yellow), M (magenta), and C (cyan). The image data is converted into image data for image formation and output to the laser driving circuit DL at a predetermined timing. The laser drive circuit DL outputs a laser drive signal to the latent image forming device ROS (optical scanning device) according to the input image data of each color. The ROS emits laser beams (image writing light) Ly, Lm, Lc, and Lk for image writing of each color according to a laser drive signal.

A developer replenishing device Ua for replenishing toner (developer) is disposed above the ROS. In front of the ROS, toner image forming apparatuses UK, UY, UM, and UC for forming toner images of K (black), Y (yellow), M (magenta), and C (cyan) are disposed. Around the drum-shaped photoreceptor (primary toner image carrier) Pk of the K (black) toner image forming apparatus UK, a charging roll CRk as a charger, a developing device Gk, and an image carrier developer adsorbing and holding are provided. Members CLk and the like are arranged.
Further, around the photosensitive members (primary toner image carriers) Py, Pm, and Pc of other toner image forming apparatuses UY, UM, and UC, chargers CRy, CRm, CRc, developing devices Gy, Gm, and Gc, a toner adsorbing / holding member CLy, CLm, and CLc for the photosensitive member are arranged.

An intermediate transfer device Ut is disposed in front of the toner image forming devices UY, UM, UC, UK. The intermediate transfer device Ut includes three intermediate transfer drums (intermediate toner image carriers) DR1, DR2, and DR3. The first intermediate transfer drum (primary intermediate toner image carrier) DR1 is in contact with the Y color photoreceptor Py in the primary transfer area Qy and in contact with the M color photoreceptor Pm in the primary transfer area Qm. The second intermediate transfer drum (primary intermediate toner image carrier) DR2 is in contact with the C-color photoconductor Pc in the primary transfer area Qc and in contact with the K-color photoconductor Pk in the primary transfer area Qk. The third intermediate transfer drum (secondary intermediate toner image carrier) DR3 is in contact with the intermediate transfer drums DR1 and DR2 in the intermediate transfer regions Q31 and Q32.
In front of the third intermediate transfer drum DR3, a secondary transfer roll (secondary transfer device) Rt that is in contact with the secondary transfer region Q2 is disposed to face the third intermediate transfer drum DR3. A secondary transfer roll cleaner CLt that cleans the toner on the surface of the secondary transfer roll Rt is in contact with the secondary transfer roll Rt.
Intermediate transfer drum toner suction holding members CL1 and CL2 are disposed downstream of the intermediate transfer regions Q31 and Q32 in the rotational direction of the intermediate transfer drums DR1 and DR2. Further, an intermediate transfer drum toner adsorbing / holding member CL3 is disposed downstream of the secondary transfer region Q2 in the rotation direction of the third intermediate transfer drum DR3. A bias for toner image transfer is applied to each of the intermediate transfer drums DR1 to DR3 and the secondary transfer roll Rt.

In FIG. 2, photoconductors (primary toner image carriers) Py, Pm, Pc, and Pk are uniformly charged by charging rolls CRy, CRm, CRc, and CRk, respectively, and then output from the latent image forming apparatus ROS. An electrostatic latent image is formed on the surface by the laser beams Ly, Lm, Lc, and Lk. When forming a full-color image, electrostatic latent images corresponding to four color images of Y, M, C, and K are formed on the respective photoreceptors Py, Pm, Pc, and Pk. Only the electrostatic latent image corresponding to the image of) is formed on the photosensitive member Pk.
The electrostatic latent images on the surfaces of the photoreceptors Py, Pm, Pc, and Pk are Y (yellow), M (magenta), C (cyan), and K (black) colors by the developing units Gy, Gm, Gc, and Gk. The toner image is developed. The developing devices Gy, Gm, Gc, and Gk are supplied with toner from the toner cartridges KTy, KTm, KTc, and KTk of the respective colors mounted on the toner dispenser device Ua.

  Y (yellow) and M (magenta) toner images formed on the Y-color and M-color photoconductors Py and Pm are primarily transferred to the first intermediate transfer drum DR1 in the primary transfer areas Qy and Qm. After that, the image is transferred to the third intermediate transfer drum DR3 in the intermediate transfer region Q31. C (cyan) and K (black) toner images formed on the C-color and K-color photoconductors Pc and Pk are primary-transferred on the second intermediate transfer drum DR2 in the primary transfer areas Qc and Qk. Then, in the intermediate transfer region Q32, the toner is transferred onto the Y (yellow) and M (magenta) toners of the third intermediate transfer drum DR3.

The sheets S stored in the paper feed tray TR1 are taken out by the pickup roll Rp at a predetermined timing, separated one by one by the separation roll Rs, and conveyed to the registration roll Rr by the conveyance roller Ra in the sheet conveyance path SH1. Further, the sheet S on the manual feed tray TR0 is fed by the manual feed roll Rp0 and conveyed to the registration roll Rr. The sheet conveyance path SH1 is provided on the upstream side sheet conveyance path SH1a on which the recording sheet S fed from the sheet feed tray TR1 is conveyed, and on the downstream side in the sheet conveyance direction from the upstream sheet conveyance path SH1a. A loop forming path (curved conveyance path) SH1b that is convexly curved downward. The width in the sheet thickness direction of the loop forming path SH1b is the width in the sheet thickness direction of the upstream sheet conveying path SH1a so that a loop (curve of paper) for correcting the inclination (skew) of the front end of the sheet can be formed. Is set wider than.
The recording sheet S conveyed to the registration roll Rr is conveyed to the secondary transfer area Q2 at the timing when the multiple toner image or the single color toner image moves to the secondary transfer area Q2, and is conveyed by the secondary transfer roll Rt. The toner image is secondarily transferred.

The toner remaining on the surface of each of the photoconductors Py, Pm, Pc, and Pk after the primary transfer is temporarily adsorbed and held by the photoconductor toner adsorption holding members CLk, CLy, CLm, and CLc, and the photoconductors Py, Pm. , Pc, Pk surfaces are cleaned. Similarly, the residual toner adhering to the surface of the intermediate transfer drums DR1 to DR3 after the intermediate transfer or secondary transfer is temporarily held by the intermediate transfer drum toner suction holding members CL1 to CL3 and cleaned.
The toner temporarily adsorbed and held by each of the toner adsorbing and holding members CLk, CLy, CLm, CLc, CL1 to CL3 is in the image carrier Py, Pm, Pc, Pk, in the cleaning mode started at a predetermined timing. It is discharged onto the surface of DR1 to DR3, transferred and conveyed to the secondary transfer roll Rt, and collected by the secondary transfer roll cleaner CLt. The toner collected by the secondary transfer roll cleaner CLt is conveyed through a toner discharge path (not shown) and collected in the toner collection box Bt.
A technique for cleaning by temporarily adsorbing and holding toner with a toner adsorbing / holding member is known in the art (see, for example, Japanese Patent Application Laid-Open No. 2003-029588) and adopts various configurations. Since it is possible, detailed description is abbreviate | omitted.

The recording sheet S on which the toner image is secondarily transferred in the secondary transfer region Q2 is conveyed to the fixing device F. When the recording sheet S passes through the fixing region Q5 where the heating rolls Fh and Fp of the fixing device F are pressed, the toner image is heated and fixed. The recording sheet S on which the toner image is heat-fixed is conveyed to the sheet discharge roller Rh and discharged to the discharge tray TRh.
When performing duplex printing, it is switched back by the sheet discharge roller Rh, conveyed to the sheet reversing path SH2, and retransmitted to the registration roll Rr with the front and back reversed.

(Description of sheet conveyance path)
FIG. 3 is an explanatory view of a transmission type sensor, and is an enlarged view of a main part of FIG.
FIG. 4 is an explanatory diagram of a reflective sensor.
FIG. 5 is a perspective view of a sensor support member on which the transmissive sensor and the reflective sensor of the embodiment are arranged.
FIG. 6 is an enlarged view of the main part of FIG.
2 to 4, an upstream sheet guide SG1 for guiding the recording sheet S fed from the sheet feeding tray TR1 is disposed below the upstream sheet transport path SH1a. 3 and 4, an upstream guide surface SG1a that guides in contact with one surface (image recording surface) of the recording sheet S fed from the sheet feeding tray TR1 is provided on the upper surface of the upstream sheet guide SG1. Is formed. A plurality of upstream guide ribs SG1b are formed on the upstream guide surface SG1a.

  A merging section sheet guide SG2 is disposed on the upper side of the upstream sheet conveyance path SH1a. 3 to 6, the lower guide surface that guides the lower surface of the junction sheet guide SG2 in contact with the other surface (non-image recording surface) of the recording sheet S fed from the sheet feeding tray TR1. SG2a is formed. Further, the upper surface of the merging section sheet guide SG2 is brought into contact with the recording sheet S fed from the manual feed tray TR0 or the recording sheet S which is conveyed by being reversed by the sheet reversing path SH2. An upper guide surface SG2b is formed. A plurality of joining portion sheet guide ribs SG2c are formed on the both guide surfaces SG2a, SG2b.

3-6, below the loop formation path SH1b, a loop formation path lower guide SG3 that is convexly curved downward and guides one surface of the recording sheet S (position regulation) is disposed. Above the loop forming path SH1b, a loop forming path upper guide SG4 for guiding the other surface of the recording sheet S is disposed.
On the upper surface of the loop formation path lower guide SG3, a loop formation path lower guide surface SG3a is formed which contacts and guides one surface of the recording sheet S. 5 and 6, a plurality of lower guide ribs SG3b are formed on the loop formation path lower guide surface SG3a. In FIG. 6, a detection light incident port SG3c is formed in the loop forming path SH1b in the vicinity of the registration roll Rr at the center, and a detection light incident / exit port (detection light incident) is located on the right side of the detection light incident port SG3c. Mouth) SG3d is formed.
3 to 6, a loop forming path upper guide surface SG4a is formed on the lower surface of the loop forming path upper guide SG4 so as to contact and guide the other surface of the recording sheet S. A plurality of upper guide ribs SG4b are formed on the loop forming path upper guide surface SG4a.

(Description of sheet sensor)
3 and 6, a light emitting section side case SN1a of the transmissive sensor SN1 is supported in the vicinity of the registration roll Rr on the downstream side of the loop formation path upper guide SG4. A transmissive sensor light emitting unit 1 that radiates detection light to the recording sheet S is supported on the light emitting unit side case SN1a on the loop formation path SH1b side. The light receiving unit side case SN1b of the transmission sensor SN1 is supported by the loop forming path lower guide SG3 at a position facing the light emitting unit side case SN1a. A transmissive sensor light receiving portion (light receiving portion) 2 for receiving the detection light irradiated from the transmissive sensor light emitting portion 1 and transmitted through the recording sheet S and passing through the detection light incident port SG3b to the light receiving portion side case SN1b. Is supported.
In the transmissive sensor SN1, the light quantity received by the transmissive sensor light receiving unit 2 increases as the recording sheet S is thinner. For this reason, the transmissive sensor SN1 can detect the thickness of the recording sheet S based on the amount of light received by the transmissive sensor light receiving unit 2.

4 and 6, the loop forming path lower guide SG3 supports the reflective case SN2a of the reflective sensor SN2 disposed upward on the right side (+ Y side) of the light receiving unit side case SN1b. ing. On the loop forming path SH1b side of the reflective case SN2a, a reflective sensor light emitting unit 6 that irradiates one surface of the recording sheet S with the detection light incident / exit port SG3c, and one surface of the recording sheet S A specularly reflected light receiving part (light receiving part) 7 for receiving the detection light specularly reflected by the light and a diffusely reflected light receiving part (light receiving part) 8 for receiving the detection light irregularly reflected on one surface of the recording sheet S are supported. .
In the reflective sensor SN2, the amount of specular reflection light is large when the glossiness of the surface of the recording sheet S is high, and the amount of diffuse reflection light is large when the glossiness of the surface of the recording sheet S is low. For this reason, the reflective sensor SN2 can detect the glossiness of the recording sheet S based on the amount of light received by the regular reflection light receiving unit 7 and the amount of light received by the irregular reflection light receiving unit 8.
A sheet conveying device (Ra, Rr, SH1b, SN1, SN2) is configured by the sheet conveying roll Ra, the registration roll Rr, the loop forming path SH1b, the transmissive sensor SN1, and the reflective sensor SN2.

(Operation of Example)
In the image forming apparatus U of the embodiment having the above-described configuration, the recording sheet S fed from the sheet feeding tray TR1, the recording sheet S fed from the manual feed tray TR0, or the sheet reversing path SH2 is reversed. The recording sheet S to be conveyed is conveyed to the loop forming path SH1b. The recording sheet S conveyed to the loop formation path SH1b is guided by a loop formation path upper guide surface SG4a and a loop formation path lower guide surface SG3a provided on both upper and lower sides of the loop formation path SH1b and conveyed to the registration roll Rr. Is done. The front end of the recording sheet S is abutted against the registration roll Rr and temporarily stops. Then, in a state where the front end of the recording sheet S is once stopped, the recording sheet S is bent by further rotating the sheet conveying roll Ra disposed on the upstream side in the sheet conveying direction from the registration roll Rr. At this time, in the recording sheet S, a loop is formed along the loop formation path lower guide surface SG3a that is convexly curved downward. For this reason, the skew of the recording sheet S can be corrected.
The recording sheet S is detected for sheet thickness and glossiness by a transmission sensor SN1 and a reflection sensor SN2 whose light receiving side is supported by a loop formation path lower guide SG3 disposed below the loop formation path SH1b. Is done. Then, the recording sheet S is conveyed to the secondary transfer area Q2 in time with the multiple toner image or the single color toner image moving to the secondary transfer area Q2.

  When using thin paper with low rigidity, in the sheet conveyance path curved upward as in the prior art (J03), the sensor placed above the sheet conveyance path due to the weakness of the thin paper and the action of gravity There is a possibility that a large loop to be brought into contact with cannot be formed as shown by the solid line in FIG. However, as in the present embodiment, a convexly curved loop is formed on the lower side. Therefore, even with a low rigidity sheet such as the thin paper, due to the weakness of the sheet and the action of gravity, as in the prior art (J03) The loop is not recessed, and is pressed against the loop formation path lower guide surface SG3a. For this reason, the distance between one surface of the various sheets and the transmissive sensor light receiving unit 2 can be made constant, and the distance between the one surface of the sheet and the reflective sensor light receiving units 7 and 8 can be made constant. Therefore, the transmissive sensor SN1 and the reflective sensor SN2 of this embodiment can accurately detect various sheets.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is performed within the range of the summary of this invention described in the claim. It is possible. Modified examples (H01) to (H02) of the present invention are exemplified below.
(H01) In the above-described embodiment, the present invention is not limited to a printer, but can be applied to an image forming apparatus such as a FAX or a multifunction peripheral. Further, the present invention is not limited to a color image forming apparatus, and can be applied to a monochrome image forming apparatus.
(H02) In the above embodiment, the present invention is not limited to the sheet thickness sensor and the sheet gloss sensor, and can be applied to a sheet position sensor.

1 is a perspective explanatory view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an overall explanatory diagram of the image forming apparatus according to the first exemplary embodiment. FIG. 3 is an explanatory view of a transmission type sensor, and is an enlarged view of a main part of FIG. FIG. 4 is an explanatory diagram of a reflective sensor. FIG. 5 is a perspective view of a sensor support member on which the transmissive sensor and the reflective sensor of the embodiment are arranged. FIG. 6 is an enlarged view of the main part of FIG. FIG. 7 is an explanatory diagram of a conventional sheet sensor.

Explanation of symbols

2, 7, 8, light receiving part S, sheet SG 3, sensor support member SH 1 b, curved conveyance path SN 1, SN 2, sheet sensor Ra, Rr, SH 1 b, SN 1, SN 2, sheet conveyance apparatus U, image forming apparatus

Claims (4)

A sheet sensor comprising the following structural requirements (A01), (A02) , and (A02a) :
(A01) provided at the upstream side of a registration roll for temporarily stopping the front end of the conveyed sheet and curving the sheet to correct the inclination of the sheet and then conveying the sheet downstream in the sheet conveying direction; And a sheet sensor disposed on the protruding surface side of the sheet that is conveyed in a curved state along a curved conveying path that is curved so as to protrude downward.
(A02) The sheet sensor having a light receiving unit that detects sheet detection light applied to the sheet temporarily stopped in the curved conveyance path and is supported by a sensor support member ;
(A02a) a light emitting unit that irradiates the sheet with the sheet detection light, and the light receiving unit that receives light from the sheet irradiated with the sheet detection light,
Both the light emitting part and the light receiving part are arranged in a lower guide that guides and contacts a lower surface of the sheet that is convexly curved downward, and
The light emitting unit and the light receiving unit are arranged along a conveyance direction of the sheet
The sheet sensor. The sheet sensor according to claim 1, comprising the following structural requirements (A03):
(A03) The sheet sensor including the light receiving unit disposed facing upward and facing the sheet. A sheet conveying apparatus comprising the sheet sensor according to claim 1. An image forming apparatus comprising the sheet conveying device according to claim 3.

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