WE CLAIM:
[Claim 1] A double acting fluid pressure cylinder (20, 20A, 120, 120A)
comprising a cylinder main body (36, 136) in which a piston (38, 138)
reciprocates,
wherein the cylinder main body (36, 136) includes
a switch valve (24, 124) including a discharge port (28, 128),
a supply check valve (30, 130),
a flow path (60, 62, 64, 68, 80) connecting one cylinder chamber (42,
142) with a fluid supply source (26, 126) and connecting the other
cylinder chamber (44, 144) with at least the discharge port (28, 128)
when the switch valve (24, 124) is at a first position, and
a flow path (60, 62, 64, 72, 74, 80) connecting the one cylinder
chamber (42, 142) with the other cylinder chamber (44, 144) via the
supply check valve (30, 130) and connecting the one cylinder chamber
(42, 142) with at least the discharge port (28, 128) when the switch
valve (24, 124) is at a second position.
[Claim 2] The fluid pressure cylinder (120, 120A) according to claim 1, wherein
the switch valve (124) is arranged at an upper portion of the one cylinder chamber (142), or at sides of the one cylinder chamber (142) and the other cylinder chamber (144).
[Claim 3] The fluid pressure cylinder (20, 20A, 120, 120A) according to claim 1
or 2, wherein a first tank (34, 134) is arranged between the other cylinder chamber (44, 144) and the switch valve (24, 124).
[Claim 4] The fluid pressure cylinder (120, 120A) according to claim 3, wherein
the first tank (134) is arranged at an upper portion of the other cylinder chamber (144) or at a lower portion of the switch valve (124).
[Claim 5] The fluid pressure cylinder (20, 20A, 120, 120A) according to claim 3
or 4, wherein a volume of the first tank (34, 134) is approximately half a maximum value of a fluctuating volume of the one cylinder chamber (42, 142).
[Claim 6] The fluid pressure cylinder (20, 20A, 120, 120A) according to any one
of claims 3 to 5, wherein a throttle valve (32, 132) is arranged at the discharge port (28, 128).
[Claim 7] The fluid pressure cylinder (20, 20A, 120, 120A) according to claim 6,
wherein the throttle valve (32, 132) is a variable throttle valve.
[Claim 8] The fluid pressure cylinder (20A, 120A) according to claim 6 or 7,
wherein:

a second tank (84, 184) is further arranged and is connected to the throttle valve (32, 132) in parallel with respect to the switch valve (24, 124);
when the switch valve (24, 124) is at the first position, the other cylinder chamber (44, 144) communicates with the throttle valve (32, 132) and the second tank (84, 184) via the switch valve (24, 124); and when the switch valve (24, 124) is at the second position, the one cylinder chamber (42, 142) communicates with the other cylinder chamber (44, 144) via the supply check valve (30, 130) and the switch valve (24, 124), and communicates with the throttle valve (32, 132) and the second tank (84, 184) via the switch valve (24, 124).
[Claim 9] The fluid pressure cylinder (20A, 120A) according to claim 8, wherein
a pressure accumulator check valve (86, 186) is arranged between the switch valve (24, 124) and the second tank (84, 184).
[Claim 10] The fluid pressure cylinder (20A, 120A) according to claim 8 or 9,
wherein a first fluid supply mechanism (88, 188) is further arranged and is configured to supply a fluid accumulated in the second tank (84, 184) to the other cylinder chamber (44, 144) when the switch valve (24, 124) is at the second position and when part of a fluid accumulated in the one cylinder chamber (42, 142) is supplied from the one cylinder chamber (42, 142) to the other cylinder chamber (44, 144) via the supply check valve (30, 130) and the switch valve (24, 124),.
[Claim 11] The fluid pressure cylinder (20A, 120A) according to claim 10,
wherein a second fluid supply mechanism (92, 192) is further arranged and is configured to supply fluid from the fluid supply source (26, 126) to the second tank (84, 184).
[Claim 12] The fluid pressure cylinder (120A) according to claim 11, wherein:
the first tank (134) and the second tank (184) are arranged in parallel inside the cylinder main body (136);
the switch valve (124) is arranged at an upper portion of the first tank (134), and an air-operated valve (194) is arranged at an upper portion of the second tank (184) and constitutes the second fluid supply mechanism (192); and
the piston (138), the one cylinder chamber (142), and the other cylinder chamber (144) are arranged between the switch valve (124) and the air-operated valve (194).
[Claim 13] The fluid pressure cylinder (120A) according to claim 12, wherein the
piston (138) has an elliptical shape along a vertical direction.

[Claim 14] The fluid pressure cylinder (120A) according to claim 12 or 13,
wherein:
a magnet (196) is disposed at an upper portion of the piston (138); and magnetic sensors (198a, 198b) configured to detect magnetism of the magnet (196) are disposed near the one cylinder chamber (142) and the other cylinder chamber (144) in the cylinder main body (136), re-spectively.
[Claim 15] The fluid pressure cylinder (120A) according to any one of claims 12 to
14, wherein the first tank (134) and the second tank (184) have ap-proximately same volume.