Chapter 2 THEORY OF OPERATION
2 - 2
Bearing is press fitted to the Force Plate/Insert Assembly to accommodate the other end of
the Leadscrew.
A Shaft is attached to the Motor Plate Assembly and to the Force Plate/Insert Assembly
using two screws. This shaft guides the Plunger Driver back and forth in its range of travel
while helping to keep the Plunger Driver Assembly from rotating perpendicularly in relation
to the direction of infusion travel. The Motor Plate Assembly and Force Plate/Insert
Assembly are both locked to the Chassis. Finally, much of the Mechanical Drive Assembly
is sealed with RTV. Rotational mechanics of the Drivetrain are as follows:
• Rotation of the Micro-Mo Motor turns a 22-tooth Gear attached to the Gearbox output
shaft with a setscrew. Another 22-tooth Gear is attached to the Leadscrew shaft and
meshes with the 22-tooth Gear on the output shaft. The gear on the Leadscrew shaft
causes rotation of the Leadscrew.
• Movement of the syringe plunger results when the Leadscrew turns against the Halfnuts
causing the Plunger Driver Assembly to traverse along the Leadscrew.
2.1.1.4 Plunger Capture Sensor
The Soft Pot Bracket Assembly and Drive Actuator Assembly contribute functionally to the
Syringe Recognition process. The Soft Pot Bracket Assembly, consisting of a Drive
Potentiometer attached to the Soft Pot Bracket, attaches with one screw to the Motor Plate
Assembly and with two screws to the Load Plate Assembly. Tabs are located on both
Motor Plate and Load Plate Assemblies for correct positioning and seating of the Soft Pot
Bracket Assembly to both Motor Plate and Load Plate Assemblies. The Drive Actuator
Assembly, consisting of a Wiper Spring assembled to the Wiper Support, rides in a “V”
shaped slot in the Plunger Driver Carriage.
Two cams on the Plunger Driver Lever are used to position the Wiper Support. As the
Lever rotates, the Drive Actuator Assembly will move back and forth in the Carriage V slot.
When the Slide is closed (i.e. pulled by the Constant Force Spring all the way into the
Mechanical Drive Assembly), the Lever Pin will end up being in the bottom of the short
dogleg slot on the Plunger Driver Slide. When in either the long or short dogleg of the
Slide, the Lever Pin causes the Lever to rotate in a manner such that the Lever’s Wiper
Support cams position the Wiper Support and the Wiper Spring a precise distance away
from the Drive Potentiometer. The Wiper Spring has three leaf springs on it. The middle
spring is the part of the Wiper Spring that can make contact with the Drive Potentiometer
and cause it to activate. The two outer springs are used to push the Wiper Support and
Wiper Spring away from the Drive Potentiometer. The Drive Potentiometer has two
polyester layers that are conductive on one side and are separated by a thin polyester and
adhesive spacer. When the Wiper Spring moves close enough to the Drive Potentiometer,
the two Drive Potentiometer conductive layers come into contact causing the Drive
Potentiometer to actuate. When the Slide is closed, the Wiper Spring moves away from
the Drive Potentiometer and the middle Wiper Spring is not able to cause the Drive
Potentiometer to activate. Mechanics of the syringe plunger detection feature, including
“Timing,” are as follows:
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