Article transport facility

1 . An article transport facility comprising:

a pair of travel rails extending along a travel route;

a transport vehicle configured to travel along the travel route and transport an article;

a guide rail configured to guide a direction of travel of the transport vehicle in a branch-junction section in which the travel route branches and joins another route; and

a control system configured to control the transport vehicle,

wherein the transport vehicle comprises:

travel wheels configured to roll on upper surfaces of the pair of travel rails;

a guide wheel configured to roll on a first-side surface or a second-side surface of the guide rail, the first-side surface facing a first side Y 1 and the second-side surface facing an opposite second side Y 2 in a width direction Y orthogonal to a travel direction X extending along the travel route; and

a guide wheel drive unit configured to move the guide wheel in the width direction Y between a first position at which the guide wheel rolls on the first-side surface and a second position at which the guide wheel rolls on the second-side surface,

wherein the branch-junction section comprises:

a first section;

a second section extending side by side with the first section; and

a connecting section connecting the first section and the second section,

wherein the connecting section branches off from the first section toward the first side Y 1 in the width direction Y and joins the second section from the second side Y 2 in the width direction Y,

wherein the guide rail comprises:

a branch guide portion spanning from the first section to an intermediate position in the connecting section;

a junction guide portion spanning from an intermediate position in the connecting section to the second section; and

a switching area, located along the travel direction X, configured to allow the guide wheel to move, in the width direction Y, between the branch guide portion and the junction guide portion,

wherein in a case where the transport vehicle travels through the branch-junction section:

the control system is configured to execute preliminary biasing processing including controlling the guide wheel drive unit to bias the guide wheel in a direction from the first position toward the second position while the guide wheel is at the first position and is in contact with the first-side surface of the branch guide portion from the first side Y 1 in the width direction Y prior to entering the switching area, and

the control system is further configured to cause the guide wheel to move in the switching area by executing the preliminary biasing processing to keep the guide wheel in contact with the first-side surface from the branch guide portion to the switching area.

2 . The article transport facility according to claim 1 ,

wherein, in the case where the transport vehicle travels through the branch-junction section:

the control system is configured to control the guide wheel drive unit to place the guide wheel at the first position (i) prior to the preliminary biasing processing being executed and (ii) prior to the guide wheel entering the first section, such-se that the guide wheel comes into contact with the first-side surface of the branch guide portion from the first side Y 1 in the width direction Y subsequent to the guide wheel entering the first section, and

the control system is further configured to cause the guide wheel to pass through the switching area while the preliminary biasing processing is being executed to move the guide wheel from the first position to the second position in the switching area and bring the guide wheel into contact with the second-side surface of the junction guide portion from the second side Y 2 in the width direction Y.

3 . The article transport facility according to claim 1 , wherein:

the travel wheels comprise a plurality of travel wheels spaced apart from each other in at least either the travel direction X or the width direction Y,

the control system comprises a determination unit configured to determine that the guide wheel has come into contact with the branch guide portion subsequent to the guide wheel entering the first section,

the determination unit is configured to determine that the guide wheel has started to come into contact with the branch guide portion in response to a rotation speed difference between rotation speeds of two or more target travel wheels spaced apart from each other in the travel direction X or the width direction Y, changing by an amount greater than or equal to a prescribed threshold value, and

the control system is configured to execute the preliminary biasing processing based on a result of determination performed by the determination unit.

4 . The article transport facility according to claim 3 , wherein:

the pair of travel rails comprise a first travel rail on the first side Y 1 in the width direction Y and a second travel rail on the second side Y 2 in the width Y direction,

the plurality of travel wheels comprise:

a first front wheel configured to roll on an upper surface of the first travel rail;

a first rear wheel configured to roll on the first travel rail behind the first front wheel in a direction of travel;

a second front wheel configured to roll on an upper surface of the second travel rail; and

a second rear wheel configured to roll on the second travel rail behind the second front wheel in the direction of travel, and

the rotation speed difference is a difference between (i) a rotation speed of at least one of the first rear wheel and the second rear wheel and (ii) a rotation speed of at least one of the first front wheel and the second front wheel.

5 . The article transport facility according to claim 3 ,

wherein the control system is configured to execute the preliminary biasing processing subsequent to the determination unit determining that the guide wheel has started to come into contact with the branch guide portion and prior to the transport vehicle having traveled a predetermined distance.

6 . The article transport facility according to claim 3 ,

wherein the control system is configured to execute the preliminary biasing processing immediately subsequent to the determination unit determining that the guide wheel has started to come into contact with the branch guide portion.

7 . The article transport facility according to claim 1 ,

wherein the transport vehicle comprises:

a front travel portion comprising a front wheel as one of the travel wheels;

a rear travel portion comprising a rear wheel as one of the travel wheels;

a front guide wheel serving as the guide wheel in the front travel portion; and

a rear guide wheel serving as the guide wheel in the rear travel portion, and

wherein the control system is configured to execute the preliminary biasing processing simultaneously on both the front guide wheel and the rear guide wheel (i) subsequent to the rear guide wheel starting to come into contact with the branch guide portion and (ii) prior to the front guide wheel entering the switching area.

8 . The article transport facility according to claim 1 ,

wherein the transport vehicle comprises:

a front travel portion comprising a front wheel as one of the travel wheels;

a rear travel portion comprising a rear wheel as one of the travel wheels;

a front guide wheel serving as the guide wheel in the front travel portion; and

a rear guide wheel serving as the guide wheel in the rear travel portion, and the control system is configured to execute the preliminary biasing processing on the front guide wheel subsequent to the front guide wheel starting to come into contact with the branch guide portion, and is further configured to execute the preliminary biasing processing on the rear guide wheel (i) subsequent to the rear guide wheel starting to come into contact with the branch guide portion and (ii) subsequent to the control system executing the preliminary biasing processing on the front guide wheel.

9 . The article transport facility according to claim 1 ,

wherein the first-side surface is curved continuously from the branch guide portion to the switching area.