MTS Series 242 Actuators - Manual (Page 16)

Series 242 Actuator Product Information 16
Series 242 Actuator Component Identification
Introduction
Series 242 Actuator Component Descriptions
C OMPONENT D ESCRIPTION
Piston rod The actuator is equipped with a double-ended piston rod. The double-ended piston has
equal areas on both sides for balanced performance. It is machined from a single piece
of heat-treated alloy steel, hard-chrome plated, and precision ground to a fine finish for
reliable operation. The piston rod is hollow to allow for installation and accurate
alignment of a displacement transducer.
Piston rod seal One low-pressure seal assembly in each end cap contains a seal to guide excess fluid to
the drainback port and a wiper to prevent external contamination from entering the
actuator.
Piston rod
bearings These high-capacity nonmetallic bearings are bonded directly to the end caps. The
nonmetallic bearings are standard due to their high sideload tolerance and resistance to
failure from galling and seizure.
The close tolerance fit between the piston rod and bearing surface creates a low leakage
viscous seal. A small amount of hydraulic fluid is allowed to flow across the bearing for
lubrication, and is then ported back to the system hydraulic reservoir.
Extension port/
Retraction port Ports allow fluid flow up to 57 L/m (15 gpm) for high-velocity or high-frequency
operation. Internal passages are designed to minimize fluid flow restrictions.
High-pressure hydraulic fluid is ported into the cylinder through the retraction port or
the extension port. The flow is regulated by a servovalve. As hydraulic pressure is
applied to one port, the other port is opened to a return line causing the actuator to
extend or to retract.
Spacer tube Extends the pedestal base to accommodate different actuator displacements.
LVDT connector Connects the LVDT to the system controller. The controller provides an excitation
signal and the LVDT returns a feedback signal. The feedback signal indicates the
actuator displacement to the controller.
Pedestal base The pedestal base allows the actuator to be rigidly mounted to a reaction mass, or
permits attachment of a swivel mounting accessory. The base is also used to mount the
LVDT connector receptacle and LVDT coil locking collar.
LVDT assembly The internally mounted LVDT indicates the actuator piston rod displacement. The
LVDT consists of a coil, core, and core extension. The core is secured to the piston rod
by a core mount. The core extension is secured to the inside of the hollow piston rod by
a locking setscrew, and can be adjusted to establish a zero reference point for the
actuator.
Drainback port The drainback port allows fluid that manages to leak past the seals to be routed out of
the actuator. This prevents pressure pockets from interfering with the actuator
performance.
Cushions Hydraulic cushions protect the end caps during full-stroke, high-velocity operation.
Viscous piston
seal The close tolerance fit between the piston and cylinder provides an effective viscous
seal. Grooves on the piston ensure lubrication of the piston surface during short-stroke,
sideloaded tests.
Piston rod end The piston rod end has a center position internal thread and a circular pattern of
threaded holes for mounting load cells, swivels, and interface fixtures.