Quinton ST 55, Service Manual

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Cardiac Stress Treadmills Service Manual Theory of Operation 2-2
Headframe Assembly
The headframe assembly consists of the following components:
• Input power module
• Drive board assembly
• Transformer assembly
• Drive motor assembly
• Grade motor assembly
• Grade system consisting of a pinion shaft, rack gears, feedback
potentiometer, and limit switches.
Input Power Module
The input power module receives line power from the power outlet. All
treadmills sold for use in the United States and Canada use 115 or 230
VAC power. All units sold for use in Europe use 230 VAC power. The
power input module also has a connector for use with the emergency stop
switch. The emergency stop switch is an optional item on non-CE-marked
units but is standard on units sold with the CE mark.
Drive Board
The drive board on the AC Drive Module uses line power to develop 300
VDC that is then used to create three-phase power for the drive motor
assembly. The frequency of the three-phase signal sent to the drive motor
determines the drive motor rotational speed. The motor current draw is a
function of the torque load placed on the motor through the deck
assembly by the user.
The drive board on the AC Drive Module also uses AC power to generate
a half wave rectified signal used to drive the grade motor. Two solid state
relays drive the grade motor: one in the direction of increasing grade, the
other in the direction of decreasing grade.
Transformer Assembly
The transformer provides electrical isolation between the primary and
secondary voltages. It also provides stepped down voltages for use with
the control electronics.
Drive Motor Assembly
The drive motor, which is driven by the drive board, delivers torque and
speed to the front roller of the treadmill through a poly-V drive belt and a
set of appropriate speed reduction pulleys. A flywheel, integral to the
motor poly-V pulley, is used to average the pulsing runner loads.
Grade Motor Assembly and System
The grade motor drives the grade pinion shaft using a chain and a set of
speed reduction sprockets. The grade pinion shaft in turn drives a set of
rack gears, which raise and lower the front of the treadmill.