Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 54 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
4.2.5.14 AZ, ALT and CASS Drive Motors and Brakes
Brushless Motors were selected for the mount’s axes movement. For Azimuth, four (4) 5,000
RPM, 10 HP motors were selected. For Altitude, two (2) 0.17 HP, 1/3 RPM frameless
torquer motors were selected. For Cassegrain three (3) 1.3 HP, 3800 RPM brushless motors
were selected. Refer to Figure 4.2.2.8.A, B & C for representative photographs of the axis
motors.
The brushless digital motor controllers obtain shaft position information from an integral
encoder to accomplish commutation of the motors. For Azimuth and Cassegrain Rotator, the
position information comes from an absolute resolver. For Altitude the position information
comes from Hall Sensors and from a Heidenhain Interpolation box (per motor) that digitises
the optical tape encoder sinusoidal signals. The amplifiers commutate the DC voltage to
create a rotating magnetic field.
The Azimuth and Cassegrain axes motors have DC tachometers installed to provide velocity
feedback information for the Rate Loop boards to close the velocity loop. For the Altitude
motors, the optical tape encoders are used by electronics in the AZ/ALT PDU CCU to
produce an analogue voltage representative of the altitude motor’s speed.
Each motor has an integral thermostat contact that opens if the motor overheats. When this
occurs, the motor controller enable is removed, while the other motor(s) in the axis continue
to remain operational. The status of this switch is reported to and displayed at the MCU and
to the appropriate LCU. The thermostat contact automatically reset once the windings of the
motor have cooled off.
These motors have military circular connectors that allow ease of replacement (with the
obvious exception of the Altitude motors). The AZ and Cassegrain motors employ sealed
bearings that do not require greasing. The motors are rated with an IP67 sealing
specification.
VertexRSI will be using pneumatic brakes for all the axes.
The fundamental concept of brakes supplied by VertexRSI is that they are spring actuated,
failsafe brakes. That is, the brakes will only release the mount for movement when voltage is
applied to the brake control valve. Alternatively, loss of power will apply the brakes.
Pressure sensors are used to indicate to the Mount Control System when the brake has the
necessary compressed air to disengage the brake. If the pressure sensor fails to indicate this
condition, a brake fault is issue to the appropriate PDU and the axis enable command is
removed. The brake fault condition is reported to the MCU, LCU and to the PMU 2-line
LCD display.