Image recording apparatus

1. An image recording apparatus comprising:

a transfer unit having a transfer surface for holding a recording medium and configured to transfer the recording medium held on the transfer surface;

a recording head opposed to the transfer unit and configured to record images on the recording medium transferred by the transfer unit;

at least one suction-force changing unit configured to draw the recording medium;

a support member provided at substantially the same height as the transfer surface of the transfer unit and supporting the suction-force changing unit; and

a suction unit configured to draw the recording medium to a surface of the support member, via the suction-force changing unit,

wherein:

the suction-force changing unit includes an air passage unit that includes an opening area, and enables air to be drawn from the recording medium side to the suction unit side, and a valve that opens or closes the opening area of the air passage unit in accordance with a pressure difference between the recording medium side and the suction unit side;

the valve closes the air passage unit, setting the opening area of the air passage unit to value B (0<B), when the pressure in the suction unit side is lower than the pressure at the recording medium side, and opens the air passage unit, setting the opening area of the air passage unit to value A (B<A), when the pressure at the recording medium side approaches the pressure in the suction unit side; and

the suction-force changing unit draws air from the recording medium side to the suction unit side through the air passage unit having the opening area B, thereby opening the valve that closes the air passage unit because the pressure in the suction unit side is lower than the pressure at the recording medium side, thus lowering the pressure at the recording medium side toward the pressure in the suction unit side.

2. The image recording apparatus according to claim 1 ,

wherein the air passage unit includes a first opening and a second opening that differ from each other in terms of opening area,

the valve is configured to open and close the first opening, and

the valve and the air passage unit are so shaped that the opening area of sum of the first and second openings is defined as A when the valve opens the first opening, and the opening area of sum of the first and second openings is defined as B when the valve closes the first opening.

3. The image recording apparatus according to claim 2 , wherein the second opening has the opening area smaller than the opening area of the first opening.

4. The image recording apparatus according to claim 2 ,

wherein the second opening of the air passage unit comprises a plurality of openings,

and the second opening area that is a sum of the opening areas of the plurality of openings is smaller than the opening area of the first opening.

5. The image recording apparatus according to claim 4 ,

wherein the plurality of openings have different opening areas.

6. The image recording apparatus according to claim 2 , further comprising:

an opening-area changing mechanism configured to change the opening area of the second opening.

7. The image recording apparatus according to claim 6 ,

wherein the opening-area changing mechanism includes a closing member configured to cover a part of the second opening, and

a control unit configured to control the closing member, controlling the covering of the second opening.

8. The image recording apparatus according to claim 7 ,

wherein the control unit controls the closing member in accordance with a speed at which the transfer unit transfers the recording medium, thereby changing the opening area of the second opening.

9. The image recording apparatus according to claim 7 ,

wherein the control unit controls the closing member, increasing the opening area of the second opening when the transfer unit transfers the recording medium at high speed, and decreasing the opening area of the second opening when the transfer unit transfers the recording medium at low speed.

10. The image recording apparatus according to claim 2 ,

wherein the second opening provides a gap when the valve closes the first opening in part, and a porous member is arranged in the gap.

11. The image recording apparatus according to claim 1 , wherein:

the air passage unit includes an air passage member having the first opening, a second opening having an opening area smaller than the opening area of the first opening;

the valve is configured to open and close the first opening;

the second opening is provided at the valve.

12. The image recording apparatus according to claim 1 ,

wherein the valve closes a part of the air passage unit, and

the valve and the air passage unit are so shaped that the opening area of the air passage unit is defined as A when the valve opens the air passage unit, and the opening area of a gap between the valve and the air passage unit is defined as B when the valve closes the air passage unit.

13. The image recording apparatus according to claim 1 ,

wherein the valve includes a flat-plate like member configured to open and close the air passage unit,

a support member supporting the valve and allowing the valve to rotate between an opened position and a closed position, and

a balancer formed integral with the valve and opposed to the valve across the support member, and the valve opens the opening by virtue of the weight of the balancer, while the suction-force changing unit is not worked.

14. The image recording apparatus according to claim 13 ,

wherein the valve opens the air passage unit by virtue of the weight of the balancer when no pressure difference exists between the suction unit side and the recording medium side which are isolated by the flat-plate like member located at a specific position and closing the air passage unit.

15. An image recording apparatus comprising:

a transfer unit having a transfer surface for holding a recording medium and configured to transfer the recording medium held on the transfer surface;

a recording head opposed to the transfer unit and configured to record images on the recording medium transferred by the transfer unit;

at least one suction-force changing unit configured to draw the recording medium;

a support member provided at substantially the same height as the transfer surface of the transfer unit and supporting the suction-force changing unit; and

a suction unit configured to draw the recording medium to a surface of the support member, via the suction-force changing unit,

wherein:

the suction-force changing unit includes a plurality of air passage units which are provided between the recording medium side and the suction unit side and which serve to draw air toward the suction unit, and a valve that opens or closes only some of the air passage units;

the valve closes some of the air passage units when the pressure in the suction unit side becomes lower than the pressure at the recording medium; side and

a pressure difference between the recording medium side and the suction unit side decreases as air is drawn from the recording medium side toward the suction unit side, and the valve opens some of the air passage units, when air is drawn from the recording medium side toward the suction unit side through the other air passage units not closed by the suction-force changing unit, immediately after the suction unit is covered with the recording medium transferred.

16. An image recording apparatus comprising:

a transfer unit having a transfer surface for holding a recording medium and configured to transfer the recording medium held on the transfer surface;

a recording head opposed to the transfer unit and configured to record images on the recording medium transferred by the transfer unit;

at least one suction-force changing unit configured to draw the recording medium;

a support member provided at substantially the same height as the transfer surface of the transfer unit and supporting the suction-force changing unit;

a suction unit configured to draw the recording medium to a surface of the support member, via the suction-force changing unit;

a first air passage unit provided in the suction-force changing unit and enabling air to flow between the recording medium side and the suction unit side;

a valve configured to open and close the first air passage unit by virtue of a pressure difference between the recording medium side and the suction unit side;

a second air passage unit provided in the suction-force changing unit and configured to draw air from the recording medium side toward the suction unit side and thereby decrease the pressure difference between the recording medium side and the suction unit side in order to open the first air passage unit, when the recording medium covers the suction unit in a state where the valve closes the first air passage unit.