Balancer cylinder and workpiece-conveying apparatus in which balancer cylinder is used
When pressurized fluid is not supplied into or discharged from the first channel 28 a of the piston rod 28 , that is, when the first channel 28 a is isolated from the outside, the cylinder tube 22 is in a stopped state. At this time, fluid inside the first cylinder chamber 36 a is compressed, and the pressure is increased accordingly to match the sum of the weights of the cylinder tube 22 , the table 18 , and the workpiece W.
1. A balancer cylinder mounted on a workpiece carrying apparatus including a pressurized fluid supply source, the balancer cylinder being mounted with an axial direction of the balancer cylinder extending vertically, the balancer cylinder comprising:
a cylinder tube including a cylinder chamber, both ends of the cylinder chamber being closed by a head cover and a rod cover;
a piston configured to partition the cylinder chamber into a first cylinder chamber adjacent to the rod cover and a second cylinder chamber adjacent to the head cover;
a piston rod in which a channel connects the pressurized fluid supply source and the first cylinder chamber to each other, the piston rod including a first end portion connected to the piston, and a plurality of locking grooves formed on an outer circumferential surface of the piston rod;
a movable valve provided to be displaceable in the axial direction of the piston rod; and
a locking member provided in the movable valve and selectively engaging with one of the locking grooves, wherein
at a position near an end of descending stroke of the cylinder tube, when the rod cover comes into contact with the movable valve and moves an engagement position of the locking member from one of the locking grooves to another of the locking grooves, the channel connecting the pressurized fluid supply source and the first cylinder chamber to each other is closed.
2. The balancer cylinder according to claim 1 , wherein
the piston includes:
a pin accommodating hole passing through the piston in the axial direction; and
a releasing pin accommodated in the pin accommodating hole to be displaceable in the axial direction, and including a first end portion facing the first cylinder chamber and a second end portion facing the second cylinder chamber,
the rod cover includes a communication path configured to connect the first cylinder chamber and the pressurized fluid supply source to each other, and
at a position near an end of ascending stroke of the cylinder tube, due to pressurized fluid supplied from the communication path to the first cylinder chamber, the head cover pushes the movable valve via the releasing pin and moves the engagement position of the locking member from the other of the locking grooves to the one of the locking grooves.
3. The balancer cylinder according to claim 1 , wherein a second end portion of the piston rod is secured to a support mechanism constituting the workpiece carrying apparatus.
4. The balancer cylinder according to claim 1 , further comprising, between the rod cover and the movable valve, a shock absorbing mechanism configured to absorb shock caused by contact therebetween.
5. The balancer cylinder according to claim 1 , wherein
the head cover includes:
an air hole opened in an outer circumferential surface of the head cover to connect the second cylinder chamber to an atmosphere; and
a silencing member attached to the air hole and allowing passage of air therethrough.
6. The balancer cylinder according to claim 1 , wherein
the movable valve is fitted on the piston rod in the first cylinder chamber,
the piston rod includes a plurality of sealing members configured to seal a gap between the outer circumferential surface of the piston rod and an inner circumferential surface of the movable valve, and
the plurality of sealing members include:
a first sealing member disposed at a position farther from the piston than is an opening of the channel adjacent to the first cylinder chamber; and
a second sealing member disposed at a position closer to the piston than is the opening of the channel adjacent to the first cylinder chamber.
7. A workpiece carrying apparatus comprising:
a balancer cylinder;
a support mechanism configured to support the balancer cylinder with an axial direction of the balancer cylinder extending vertically;
a pressurized fluid supply source configured to supply pressurized fluid to the balancer cylinder;
a guide configured to guide a vertical operation of a cylinder tube constituting the balancer cylinder; and
a workpiece carrying member detachably connected to the cylinder tube, wherein
the balancer cylinder includes:
the cylinder tube including a cylinder chamber, both ends of the cylinder chamber being closed by a head cover and a rod cover;
a piston configured to partition the cylinder chamber into a first cylinder chamber adjacent to the rod cover and a second cylinder chamber adjacent to the head cover;
a piston rod in which a channel connects the pressurized fluid supply source and the first cylinder chamber to each other, the piston rod including a first end portion connected to the piston, and a plurality of locking grooves formed on an outer circumferential surface of the piston rod;
a movable valve provided to be displaceable in the axial direction of the piston rod; and
a locking member provided inside the movable valve and selectively engaging with one of the locking grooves, and wherein
at a position near an end of descending stroke of the cylinder tube, when the rod cover comes into contact with the movable valve and moves an engagement position of the locking member from one of the locking grooves to another of the locking grooves, the channel connecting the pressurized fluid supply source and the first cylinder chamber to each other is closed.