Liquid ejection apparatus and liquid ejection method

1. A liquid ejection apparatus comprising:

a light projection unit configured to emit a detection beam for detecting a lifting of a recording medium conveyed along a conveyance path;

a light reception unit configured to receive the detection beam;

a liquid ejection head configured to eject liquid to the recording medium; and

at least one controller configured to,

detect the lifting of the recording medium conveyed along the conveyance path in response to the recording medium being detected at a height greater than a threshold by the detection beam, and

change the threshold in real time by detecting a thickness of the recording medium as the recording medium is being conveyed, and changing the threshold at a timing when the recording medium is detected at a conveyance position upstream of a position where the liquid is ejected by the liquid ejection head.

2. The liquid ejection apparatus according to claim 1 , wherein the detection beam is a linear laser having a width in a height direction.

3. The liquid ejection apparatus according to claim 1 , wherein the at least one controller is configured to receive recording medium information including the thickness of the recording medium, and refer to correspondence information indicating a correspondence relation between the recording medium information and the threshold to change the threshold.

4. The liquid ejection apparatus according to claim 1 , further comprising:

a thickness detection unit configured to detect the thickness of the recording medium, wherein

the at least one controller is configured to increase the threshold with an increase in the detected thickness.

5. The liquid ejection apparatus according to claim 1 , further comprising:

a conveyance position detection unit configured to detect the conveyance position of the recording medium.

6. The liquid ejection apparatus according to claim 1 , wherein the at least one controller is configured to,

measure time from a conveyance start timing of the recording medium, and

determine the timing to change the threshold based on the conveyance start timing.

7. The liquid ejection apparatus according to claim 1 , wherein the at least one controller is configured to stop a conveyance operation of the recording medium when the recording medium is detected with the height greater than the threshold by the detection beam.

8. A liquid ejection method comprising:

emitting a detection beam for detecting a lifting of a recording medium conveyed along a conveyance path;

receiving the detection beam;

detecting the lifting of the recording medium conveyed along the conveyance path in response to the recording medium being detected at a height greater than a threshold by the detection beam;

changing the threshold in real time by detecting a thickness of the recording medium as the recording medium is being conveyed, and changing the threshold at a timing when the recording medium is detected at a conveyance position upstream of a position where liquid is ejected; and

ejecting the liquid to the recording medium.

9. The liquid ejection apparatus according to claim 1 , further comprising:

a registration adjusting unit including,

a pair of registration rollers configured to correct an inclination in the recording medium and

a thickness detection unit downstream of the pair of registration rollers and upstream of the liquid ejection head, the thickness detection unit configured to detect the thickness of the recording medium.

10. The liquid ejection apparatus according to claim 9 , further comprising:

a conveyance position detection unit upstream of the liquid ejection head, the conveyance position detection unit configured to detect the conveyance position of the recording medium.

11. The liquid ejection apparatus according to claim 10 , wherein the conveyance position detection unit is immediately adjacent to and upstream of the liquid ejection head.