Article elevating device
While a controller performs an elevation operation that is at least either an operation of lowering a holder or an operation of raising the holder, the controller (i) calculates a unit elevation amount, which is an amount by which the holder is raised or lowered per unit rotation amount of the drive motor in an elevation operation range that is a range of heights of the holder in the elevation operation, in accordance with a change in a diameter of an outer circumferential surface of a belt wound around a drum due to winding and unwinding of the belt, and (ii) determines a rotation amount of a drive motor for the elevation operation based on the unit elevation amount.
1 . An article elevating device comprising:
a holder configured to hold an article;
an elevating device configured to raise and lower the holder; and
a controller configured to control the elevating device,
wherein the elevating device comprises:
a drum;
a belt that is wound around the drum in such a manner as to be capable of unwinding from the drum and wound around the drum;
a drive motor configured to drive the drum to rotate; and
a transmission mechanism configured to transmit driving force from the drive motor to the drum,
wherein the elevating device lowers the holder by unwinding the belt from the drum and raises the holder by winding the belt around the drum, while the holder is suspended with the belt, and
wherein, while the controller performs an elevation operation that is at least either an operation of lowering the holder or an operation of raising the holder, the controller (i) calculates a unit elevation amount, which is an amount by which the holder is raised or lowered per unit rotation amount of the drive motor in an elevation operation range that is a range of heights of the holder in the elevation operation, in accordance with a change in a diameter of an outer circumferential surface of the belt wound around the drum due to winding of the belt and unwinding of the belt, and (ii) determines a rotation amount of the drive motor for the elevation operation based on the unit elevation amount,
wherein the holder is initially arranged at a reference height and lowered toward a target height which is lower than the reference height before the elevation operation is performed to (i) calculate the unit elevation amount, (ii) determine the rotation amount for the elevation operation, and raise or lower the holder to the target height.
2 . The article elevating device according to claim 1 ,
wherein the controller determines the rotation amount of the drive motor by dividing a target elevation amount of the holder in the elevation operation by the unit elevation amount.
3 . The article elevating device according to claim 2 ,
wherein the controller controls the rotation amount of the drive motor based on a pulse count according to which one pulse corresponds to the unit rotation amount, and
wherein the controller calculates the unit elevation amount with use of formula (1) below,
PR =π/( RL×PP ) 2 ×( RL×PP×DL− 2× TB×UP ) (1)
where
PR is the unit elevation amount,
RL is a ratio of the rotation amount of the drive motor to a rotation amount of the drum,
PP is a pulse count corresponding to one full rotation of the drive motor,
DL is a diameter at a thickness center of an outermost turn of the belt wound around the drum while the holder is at a reference height,
TB is a thickness of the belt, and
UP is a pulse count corresponding to a rotation amount of the drive motor required to raise or lower the holder from the reference height to a height included in the elevation operation range.
4 . The article elevating device according to claim 1 , wherein:
the holder comprises a first sensor configured to detect the article at a position spaced above the article by a distance equal to a sum of a holding enabled distance and a first distance, the holding enabled distance is a relative distance between the holder and the article in an up-down direction while the holder that is in a non-holding state of not holding the article is at a position where the holder is capable of performing a holding operation of holding the article placed on at least one placement portion,
the controller gradually brings the holder in the non-holding state closer to the article on the at least one placement portion from above, causes the elevating device to perform a first operation of lowering the holder by the first distance from a position at which the article is detected by the first sensor, and causes the holder to perform the holding operation at a position in the up-down direction at which the first operation is completed, and
the elevation operation includes the first operation.
5 . The article elevating device according to claim 4 ,
wherein the at least one placement portion comprises a plurality of placement portions at different heights, and
wherein the controller sets the elevation operation range for each of the placement portions and calculates the unit elevation amount corresponding to the set elevation operation range.
6 . The article elevating device according to claim 1 , wherein:
the holder comprises:
a supporting member configured to support a supported portion of the article from below; and
a second sensor configured to detect whether the holder is (i) in a supporting state of supporting the article with the supporting member or (ii) in a non-supporting state of not supporting the article with the supporting member,
the controller gradually brings the holder that is in a holding state of holding the article closer to a placement portion for placement of the article from above, causes the elevating device to perform a second operation of lowering the holder by a second distance from a position where transition from the supporting state to the non-supporting state is detected by the second sensor as a result of the article being placed on the placement portion, and causes the holder to perform a releasing operation of retracting the supporting member from below the supported portion at a position in an up-down direction at which the second operation is completed, and
the elevation operation includes the second operation.
7 . The article elevating device according to claim 1 , wherein:
the holder comprises a third sensor configured to detect a specific state in which the holder has reached a position spaced above the article by a distance equal to a difference between a holding enabled distance and a third distance, the holding enabled distance is a relative distance between the holder and the article in an up-down direction while the holder that is in a non-holding state of not holding the article is at a position where the holder is capable of performing a holding operation of holding the article placed on a placement portion,
the controller causes the elevating device to perform a third operation of raising the holder by the third distance from a position at which the specific state is detected by the third sensor, in response to the specific state being detected by the third sensor while the holder in the non-holding state is gradually brought closer to the article on the placement portion from above, and
the elevation operation includes the third operation.
8 . The article elevating device according to claim 1 ,
wherein the transmission mechanism comprises a first shaft having a first gear and a second shaft having at least one second gear, the first shaft parallel to the second shaft, and
wherein the transmission mechanism decelerates a rotation speed of the drum with respect to the drive motor.