Drive Head; Plunger Head Board Assembly; Force Sensor Subsystem - CareFusion Alaris 8110 series Service Manual

PRINCIPLES OF OPERATION
4.6

DRIVE HEAD

The drive head captures the syringe by the
syringe plunger and uses the drivetrain to
drive the plunger in a controlled fashion.
The drive head has claw-like arms (plunger
grippers) that capture the syringe plunger.
The plunger grippers allow the drive head to
capture a wide variety of syringes (see the
Syringe or PCA Module section of the
Alaris System DFU and Set Compatibility
®
Card for more information on suitable
syringes).
To load a syringe into the drive head, the
gripper control/drive head release lever
rotates clockwise. This rotates an inner
90°
shaft, which is connected to a slide plate.
Two holes in the slide plate interface with
two pinion gears that make direct contact
with the plunger grippers. Once the slide
plate moves back, the gears rotate and the
plunger grippers open to accept the syringe
plunger flange.
Once the syringe is loaded, a plunger detect
flag interfaces with an optical switch to
indicate that a syringe is properly loaded
into the plunger grippers. The drive head
also includes a flag that indicates the drive
head position, preventing an infusion from
beginning prematurely.
Several other components of the drive head
control the opening and closing of the split
nuts on the leadscrew. A pull rod cam
attached to the end of the rotating shaft in
the drive head interfaces with a rod and
head piece that can rotate to lift the rod
attached to the drivetrain carriage and cam
lock at the other end, allowing the split nuts
to open. Once the rotating shaft rotates
clockwise to load a syringe and then
released, a torsion spring returns the gripper
control to its original position. This torsion
spring ensures that the gripper control
4-4
Alaris Syringe Module (8110 Series)
®
Alaris PCA Module (8120 Series)
®
Technical Service Manual
returns to its vertical (closed) position and
confirms that the split nuts are closed.
The drivetrain is contained in the lower and
upper housings. The lower housing is also
attached to the drive tube that connects to
the drivetrain carriage at the opposite end.
A plastic sleeve over the drive tube provides
environmental and
circuit routed up to the drive head.
4.7

PLUNGER HEAD BOARD ASSEMBLY

A strain gauge on the Plunger Head Board
senses the force applied to the syringe
plunger: the greater the force, the more
negative the amplifier output . The resulting
signal is inverted and offset on the Logic
Board.
The optical switches on the Plunger Head
Board detect whether a syringe is properly
loaded and whether the plunger grippers are
position to capture a syringe plunger. When
either optical switch is unblocked, current-
sensing circuitry on the Logic Board detects
a current from the switch.
4.8

FORCE SENSOR SUBSYSTEM

The force sensor subsystem includes a
force sensor mounted in the drive head,
rather than at the drivetrain as in other
designs.
The cantilevered force sensor contact plate
pivots on a lock plate mounted to the
underside of the lower housing. The force
sensor is positioned so that the cantilevered
contact plate acts as a moment arm from
the pivot point, providing mechanical
advantage from the syringe force to the
force sensor.
protection to the flex
ESD