DASI Motion Control System
The DASI motion control system will consist of conventional
digital quadrature encoders, and simple DC brush motors connected to a
PMAC VME
control unit.
There will be 6 encoders and 5 motors/amplifiers on 3 axis.
System Diagram
The following diagram shows the azimuth axis.
Elevation axis will be essentially the same with one encoder.
Theta axis will be essentially the same with one encoder, and
one motor.
Hardware Interlock
The hard overtravel limit switches and panic switches
will be normally closed.
A pair of wires will run from each to a patch panel on the
stationary structure.
A DC voltage will be routed through each pair of wires in series.
It will then drive the amplifier enable inputs in parallel.
In this way if any switch is activated, or panic button pushed,
all motors will stop, and all brakes will engage.
The "amplifiers" for the brake control are actually just
DC power supplies with two enable inputs.
Motors and Amplifiers
All five motors are specified to be
MCG ID34007 with tachometer
and brake.
Tachometers are normally used as feedback to velocity control amplifiers.
Do we want to use torque or velocity control?
If not used for amplifier feedback we could bring the tach signals
to ADC inputs on the PMAC for monitoring purposes (to check for
wheel slip etc).
[PMAC can do dual position/velocity servo loop but only using
a (position) encoder on the motor - not a tach. We may wish to put
MCG E9 encoders to the motors instead of tachs. These have 2000 step/rev,
which for the azimuth axis with a gear reduction ratio of 250, and
track reduction ratio of 14 corresponds to telescope motion of 0.2 arc sec.]