Belt, transfer belt unit, and image forming apparatus

1. A belt unit comprising:

a belt having an endless shape and formed of resin; and

a driving roller provided on an inner side of the belt, the driving roller rotating to cause the belt to move in a first direction, the first direction being substantially perpendicular to a widthwise direction of the belt as a second direction,

wherein the belt comprises a detection target portion on an outer surface of the belt at an end of the belt in the second direction;

wherein the detection target portion includes a plurality of grooves formed on the outer surface of the belt by laser light irradiation, the plurality of grooves being elongated in a direction substantially parallel to the first direction;

wherein the belt is stretched around a plurality of rollers including the driving roller;

wherein each of the plurality of grooves is elongated in a stretching direction of the belt, and has a depth which is less than a thickness of the belt; and

wherein among the plurality of grooves of the detection target portion, a groove located at a center of the detection target portion in the second direction has a length longer than a length of a groove located at an end edge of the detection target portion in the second direction.

2. The belt unit according to claim 1 , wherein the belt has a single-layer structure composed of resin.

3. The belt unit according to claim 1 , wherein a difference ΔY obtained by subtracting a visual reflectance Yr of the outer surface of the belt other than the detection target portion from a visual reflectance Yp of the detection target portion satisfies:

Δ Y=Yp−Yr≥ 1%.

4. The belt unit according to claim 1 , wherein the depth of each of the plurality of grooves is less than 2.3 times a mean particle diameter of a developer transferred to the belt.

5. The belt unit according to claim 1 , further comprising:

a supporting roller provided on the inner side of the belt and applying tension to the belt; and

a transfer roller that transfers a developer image to the belt.

6. An image forming apparatus comprising:

the belt unit according to claim 1 ;

an image forming unit that forms a developer image to be transferred to the belt;

a secondary transfer roller that secondarily transfers the developer image from the belt to a recording medium;

a detector that detects the detection target portion of the belt; and

a controller that controls a rotation of the driving roller based on information of detection by the detector.

7. An image forming apparatus comprising:

the belt unit according to claim 1 ;

an optical sensor that receives reflection light from the detection target portion of the belt to detect the detection target portion;

wherein the optical sensor has a receiving light spot having a diameter of α (mm), the detection target portion has a length Ld (mm) in a circumferential direction of the belt and a width Wd (mm) in the second direction; and

wherein the diameter α, the length Ld and the width Wd satisfy the following relationships:

α≤ Ld ≤ 15 mm, and 2 α≤Wd ≤ 15 mm.

8. The image forming apparatus according to claim 7 , wherein a height difference at an outer edge portion of the detection target portion is larger than a height difference at a center portion of the detection target portion.

9. The image forming apparatus according to claim 7 , wherein a distance between the detection target portion and an end edge of the belt in the second direction is larger than 1 mm.

10. The image forming apparatus according to claim 7 , wherein when a width of the belt is expressed as W (mm), a width of the recording medium is expressed as P (mm), a maximum meandering amount of the belt in the second direction during a rotation of the belt is expressed as β (mm), and a distance between the detection target portion and an end edge of the belt in the second direction is expressed as D 1 (mm), the following relationship is satisfied:

1.0 (mm)≤ D 1≤ W −(β+ Wd+P ).

11. The image forming apparatus according to claim 7 , wherein a maximum meandering amount β (mm) of the belt in the second direction during the rotation of the belt and a width Wd of the belt in the second direction satisfy:

α+2 β≤Wd≤ 15 mm.

12. The image forming apparatus according to claim 7 , wherein a height difference of the detection target portion is in a range from 2.0 μm to 10.2 μm.

13. The image forming apparatus according to claim 7 , further comprising a plurality of image forming units arranged in the first direction, each of the plurality of image forming units forming a developer image to be transferred to the belt;

wherein a plurality of detection target portions are arranged at an equal pitch in the circumferential direction of the belt, the pitch being the same as a pitch of the image forming units.

14. The belt unit according to claim 1 , wherein the detection target portion is formed on an outer circumferential surface of the belt.

15. The belt unit according to claim 1 , wherein the length of the groove located at the center of the detection target portion and the length of the groove located the end edge of the detection target portion are lengths in the stretching direction of the belt.

16. The belt unit according to claim 1 , wherein the detection target portion has a rounded corner.

17. The belt unit according to claim 1 , further comprising a cleaning member provided so as to contact the belt,

wherein when the belt moves by rotation of the driving roller, the detection target portion passes the cleaning member.

18. A belt unit comprising:

a belt having an endless shape and formed of resin; and

a driving roller provided on an inner side of the belt, the driving roller rotating to cause the belt to move in a first direction, the first direction being substantially perpendicular to a widthwise direction of the belt as a second direction,

wherein the belt comprises a detection target portion on an outer surface of the belt at an end of the belt in the second direction;

wherein the detection target portion includes a plurality of grooves formed on the outer surface of the belt by laser light irradiation, the plurality of grooves being elongated in a direction substantially parallel to the first direction;

wherein the belt is stretched around a plurality of rollers including the driving roller;

wherein each of the plurality of grooves is elongated in a stretching direction of the belt, and has a depth which is less than a thickness of the belt; and

wherein an interval between grooves of the plurality of grooves adjacent to each other is less than or equal to double a depth of the grooves.