 |
| FIG. DA03(Top view) |
| |
In double acting actuators (Fig. DA03) the output torque is the result of the pistons
force (given by the air supply pressure) multiplied by the pitch shaft radius (lever
arm) less the force lost for friction (efficiency): for this reason the output torque
is linear (Fig. DA04).
|
 |
| FIG. DA04(double acting) |
| |
For double acting actuators in normal working conditions the suggested safety
factor is 15-20%.
Air Torque actuators are designed for precise and accurate operation, maximum
machined teeth engagement, low backlash and multiple bearings on pistons to
ensure the highest level of efficiency and high cycle life.
|
| |
| |
|
SPRING RETURN ACTUATOR
(
click here to see 3D image
)
|
| |
 |
 |
| FIG. SR02(Top view) |
| |
When port 2 is pressurized and exhaust air exits from port 4, both pistons move
towards the end-caps and compress the springs (Fig. SR02) making the drive shaft
turn. For standard assembly a counter-clockwise rotation “ccw” is obtained (clockwise
rotation is possible by changing the pistons assembly). When air or electricity fails, a
fail-safe position is guaranteed by the springs force. For standard assembly a
clockwise rotation “cw” is obtained (counter-clockwise rotation is possible by
changing the pistons assembly).
In spring return actuators the output torque is the result of two operations, whose
values depend on the stroke position (0° or 90°). In spring return actuators the
output torque is the result of the force (air or springs acting on the pistons)
multiplied by the lever arm.
|
 |
| FIG. SR03(Top view) |
| |
 |
| FIG. SR04(spring return) |
| |
- First operation (Fig. SR03)
The output torque is generated by air supply pressure at Port 2 after compressing
the springs, called “OUTPUT TORQUE AIR STROKE”. In this case air forces the pistons
from the 0° to the 90° position and consequently the torque starts from a high value
and during the stroke it constantly decreases until 90° (Fig. SR04) due to the natural
force that springs generate (oppose) when they are compressed.
|
 |
| FIG. SR05(Top view) |
| |
- Second operation (Fig. SR05)
The output torque is generated by the force that springs release onto the pistons when
air fails, called “OUTPUT TORQUE SPRING STROKE”. In this case the torque, starting
from the 90° position, constantly decreases until 0° because of the springs extending
(Fig. SR06).
|
 |
| FIG. SR06(spring return) |
| |
Air Torque spring return actuators are designed to produce a balanced torque in the
two conditions explained above when the number of springs per side is equal to the
air pressure supply (4 bar - 4 springs each side) as shown in Fig. SR07.
For certain applications it is possible to achieve (where desired), the unbalanced torque
as shown in Fig. SR08, by altering the relationship between the number of springs per
side and air pressure supply in bar (for example 6 springs and 5.5 bar or vice versa).
In spring return applications two conditions can be achieved: air failure to close
or air failure to open.
The suggested safety factor for spring return actuators in normal working conditions
is 20-25%.
|
 |
| FIG. SR07 |
| |
 |
| FIG. SR08 |