Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 48 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
SIGNAL
#
SIGNAL NAME SIGNAL TYPE
36 -12V DC Low Voltage DC Power (0V on item 33)
(I) – Causes Interlock
(SF) Causes Summary Fault
(OP) – Output from LCU
DCC – Dry-Contact Closure
OCS – Open-collector sink
(*) = Standard Heidenhain Read Head 15-way D-Sub connections.
4.2.5.10 Regeneration Cabinet
Refer to Figure 4.2.2.3 for a representative photograph of the Regeneration Unit. The
Regeneration Cabinet is a free standing cabinet, used to house banks of high power resistors
needed for energy dissipation when the Azimuth, Altitude, Cassegrain and Cassegrain
CableWrap motors are being decelerated or back-driven. When a brushless motor is being
decelerated or back-driven, it pumps up the motor controller power supply buss to levels that
need to be dissipated externally in order not to incur a power supply over-voltage condition.
The Regeneration Cabinet’s high power resistors dissipate this excess energy.
For Azimuth, the braking resistors are rated for 4,000 W, 20 ohms. For Altitude, the resistors
are rated for 360 W, 25 ohms. For Cassegrain, the braking resistors are rated for 850 W, 120
ohms. For Altitude, it is anticipated that the regeneration resistors will not be used, since the
Kinetic energy of the motor/load minus the system losses will be smaller than the energy that
the Motor Controller Power Supply BUS module can store.
Thermal switches with NC contacts interface to the AZ/ALT PDU and to the CASS PDU. If
the thermal switches sense an over-temperature condition inside the power resistor enclosure,
the contacts open, signalling to the PDUs to remove the axes motor enables. When the
temperature cools off, the thermal switches automatically reset, but the axis enable command
must be re-issued to continue with axis operation.
The Regeneration resistor box has been designed to be able to handle approximately 70% of
the regeneration resistors’ heat when all of the regeneration resistors are being used
simultaneously before the thermal switch opens.
Under normal tracking conditions, due to the extremely benign axis dynamics, the average
power that the resistors will see will be dominated by the preload level (AZ and CASS) and
by the imbalance (ALT). As seen on the AD03, Motor and Brake Sizing Analysis report,
wind loading doesn’t affect AZ or CASS. Therefore the following continuous steady-state
power dissipated in the Regeneration resistors while tracking will be as follows: