THEORY OF OPERATION
4-3
Versapulse Select Service Manual
0621-499-01 01/94
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Multiplexing the beams - Merging the four Ho:YAG beam paths requires a more complicated optical
scheme. Versapulse Select uses a servo positioned rotating mirror to assemble the four Ho:YAG
beams into a single beam path. The servo system must re-position the mirror between pulses,
pointing the mirror towards the head that will be flashed.
Control - In general, the microprocessing demands of the Versapulse Select are greater than that of a
single head system. The Versapulse Select uses two Motorolla 68000 microprocessors - a main
processor and safety processor.
For the purposes of this discussion, the Versapulse Select is divided into the following functional subsystems.
The remaining topics in this section provide a detailed description of each subsystem.
Power Switching, Conditioning, Distribution (4.2) - Provides switching and conditioning of the
primary power input, converts the AC line voltage to DC voltages used within the system and
distributes the various voltages throughout. It includes the turn-on and turn-off circuitry. It does not
include the high voltage power supply (HVPS).
Cooling (4.3) - The cooling system removes heat from the Ho:YAG cavities and two beam dumps. It
is a closed loop distilled/de-ionized water system including a pump, reservoir tank, fill tank, heat
exchanger, variable speed fan, D/I filter, flow switch, temperature sensor and conductivity sensor.
Control Electronics (4.4) - The control electronics executes the software instructions to provide
overall control of the Versapulse Select. It includes a main processor (Mµp) and independent safety
processor (Sµp), associated circuits (DIO, ADC, DAC), a touch screen display, and a number of opto-
electronic and electro-mechanical devices.
Flash Lamp Supply Circuits (4.5) - The flash lamp supply starts and simmers the four flash lamps,
responds to control electronics commands to charge the main charging capacitor and to discharge the
capacitor through the selected flash lamp. It includes the HVPS, the main charging capacitor, isolated
trigger circuits, lamp select SCR's, electric field transformer, flash lamps and the simmer supply.
The flash lamps are simmered at a low current between flashes (the rods are not simmered - the flash
lamps are kept on in order to allow SCR turn on). The simmer power supply provides the simmer
current to each of the four lamps and supplies a transformer used to generate an electric field to
ionize the flash lamps.
The Ho:YAG pulses of laser energy are controlled by command signals from the control electronics.
Prior to each pulse the control electronics sends a charge command to the HVPS. The command
indicates the voltage level to which the main charging capacitor is to be charged. The higher the
capacitor charge voltage, the more energy will be produced in the laser pulse. The HVPS charges the
capacitor to the indicated voltage then sends a charge complete signal back to the control electronics.
To get a pulse of treatment energy the control electronics triggers the SCR for the cavity that has been
selected for firing. The SCR turn-on creates a discharge path for the main charging capacitor through
the selected flash lamp.
Optics (4.6) - The optics include the portions of the system that operate on the Ho:YAG beams and/
or diode aiming beam. There are four separate and identical Ho:YAG cavities arranged in a 2 x 2
matrix. Each includes a rod, flash lamp, high reflector, output coupler, and two relay mirrors. The
relay mirrors direct the Ho:YAG output from the OC towards the surface of a servo positioned
mirror. The servo positioned mirror is used to multiplex the four separate Ho:YAG beams into a
single beam path. The remainder of the beam path includes the following optical components.
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