Specifications

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Principles of Operation
The Ribbon Drive System
The ribbon drive system is controlled by the 8032 microcontroller. The
controller board sends commands to the 8032 to start and stop the ribbon, set
the ribbon speed, and apply slack or tension to the ribbon. The real–time
control functions are done by the 8032, acting in accordance with firmware
control algorithms and look–up tables. The 8032 communicates with an
ASIC to provide direct digital PWM drive signals for the ribbon motor PWM
amplifier. The 8032 drives the ribbon motors through PWM generators in the
mechanism driver integrated circuit (MDIC). Nearly all mechanical control
functions are carried out through the MDIC ASIC. Digital I/O is done
through latches connected to the 8032 I/O ports and MDIC. Ribbon faults are
passed to the controller board.
Ribbon Velocity
Ribbon velocity is controlled by means of a closed–loop system that first
measures the speed of the two ribbon drive motors. One motor is driven; the
other motor is not driven and applies tension to the ribbon through its drag
circuitry. The velocity of the driven motor is known, while the velocity of the
tensioning motor is measured by converting the zero crossing of the
back–EMF signal to a digital pulse signal. This signal is processed by the
8032 to determine the radius of the ribbon on the take–up reel. The processor
monitors this information and adjusts the velocity of the driven motor to
maintain constant linear speed. The roles of the two motors reverse at the end
of ribbon travel, when a metallic strip crosses the ribbon guide of the
emptying reel and closes a circuit that causes the RSP to reverse motor
functions.
The four PWM amplifiers in the ribbon drive system are voltage mode to aid
in system damping (as opposed to current mode). The 8032 input to the
PWM amplifiers maintains a constant voltage/frequency ratio at the motor.
The ribbon drive is protected from over current.
Ribbon Tension
The 8032 processor regulates tension in three discrete steps by using
information gathered by the zero–crossing circuitry and ribbon information.
Tension is adjusted by controlling the load on the drag motor back emf. This
load generates drag torque on the ribbon hub that maintains tension.