44
Dimples
Reference
Point
Drum Control
The drum is rotated by a belt and pulley system to a
three-phase induction motor, this is controlled by the
Motor Control Module.
When tumble drying, the drum is tumbled at 47 rpm
and at 5 rpm during opening and closing, other
speeds are used as required.
The drum’s position and speed is sensed through the
drum tacho signal, which comes via the sensor
module.
How does the drum tacho sense the position and speed of the drum?
The drum has a number of dimples that have been pressed at the drum outlet which are
spaced every 2 degrees of angle around the drum end. There is a 15-degree “gap” to
provide a reference for absolute position, which is required for the opening and closing
of the drum door.
A beam of light is directed by a lens at the arch
of the drum dimples and the amount of light
that bounces back is sensed. When the light
hits the smooth surface between the dimples it
reflects much of the light back to the light
sensor, when a dimple is hit the light is
deflected away and in this way the position of
the drum is monitored. The 15 degree “gap”
which can be located when the drum is moving
at a known speed provides the required
absolute position of the drum.
The drum’s speed and position are critical for the speed control of the drum motor by the
Motor Control Module and also for the Sensor Module for the operation of the drum door
opening and closing sequence.
Belt
Belt Tensioner
System
Three-phase
Motor
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