arecibo telescope servo drive system
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Arecibo Telescope Servo Drive System. Ideas For Computer Upgrade. (Existing) PLC hardware can be re-used to a large extent hardware (except CP581) is still will be available for many years CP581 will be removed PLC function will be limited to safety functions and low level operation

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arecibo telescope servo drive system

Arecibo Telescope Servo Drive System

Ideas For Computer Upgrade

computer upgrade concept i
(Existing) PLC

hardware can be re-used to a large extent

hardware (except CP581) is still will be available for many years

CP581 will be removed

PLC function will be limited to safety functions and low level operation

interface to servo computer via serial interface (new card) – not time critical!

New Servo Computer

Local User Interface(replaces existing LCU)


encoder readout

operating mode control

M&C Interface to host

position loops

output to DCS:analog velocity commands

Computer Upgrade Concept I
computer upgrade concept ii
Drive Control

motors to be re-used

servo amplifiers to be re-used

complete DCS to be re-used

additional setpoint from servo computer:

DCS boards can handle additional setpoint

analog signal must be wired from backplane SUB-D connector to board connector

PLC software must control selection relay


presently read by PLC

new (possibility 1)

only computer reads encoders

position dependent PLC interlocks cannot be kept

or (possibility 2)

install SSI doublers

both computer and PLC read encoders

position dependent PLC interlocks can be kept

Computer Upgrade Concept II
computer upgrade concept iii
OCU in main control room

also to be replaced

new OCU could be …

a desktop PC with keyboard and mouse, running on Windows

a rack mounted touch screen panel PC

a notebook PC

logs into servo computer via Ethernet

existing serial link no more required

Interface to host computer

remains on Ethernet


… could be kept

… or extended/modified according to present experience

… or completely changed

Computer Upgrade Concept III
possibilities for servo computer


easy replacement / upgrade

interface boards to encoders etc. to be found

existing application software to be adapted to hardware and software platform

reliability for operation unknown

becomes obsolete very fast

spare part availability

Industrial Servo Computer

proven reliability

all interface hardware available

interface modules comply to more stringent specifications

spare part availability

application software available to a large extent

prepared for future upgrades

more expensive than PC

software and drivers written for a particular hardware configuration

Possibilities for Servo Computer
vertex antenna control unit 8100
Vertex Antennentechnik’s standard controller for high accuracy antennas and telescopes since 2001

Installed at

ESA 35m Deep Space Antenna (servo accuracy ~2 mdeg)

Australia: in operation

Spain: presently being built

various (fast) ESA 15m antennas (~20 mdeg)

ALMA Radio Telescope (~0.15 mdeg)

APEX Radio Telescope (~0.15 mdeg)

AMIBA Hexapod Telescope (~3 mdeg)

CNR 32m Radio Telescopes at Noto and Medicina (~1 mdeg)

Eumetsat Polar Station, Svalbard (~20 mdeg)

various other stations

Several more installations in progress

Vertex Antenna Control Unit 8100
ALMA Prototype

at VLA site, New Mexico

ESA 35m

Deep Space Antenna,


vertex antenna control unit 810011

CompactPCI bus

VxWorks 5.5 RTOS

P III 1.3 GHz CPU with 2 Ethernet interfaces

10.4” Color Touch Screen as local user interface (separate PC running on Embedded XP)

multiple user interfaces feasible

several types of interfaces to host / encoders / drive cabinet available


drive control

fully digital Az/El drive control or

position loop only with analog velocity command output

position readout from encoders

operating modes

interlocks on software level

local control of all functions

pointing error correction (option)

communication to interlock system PLC

Interfaces to host computer

Vertex Antenna Control Unit 8100
vertex antenna control unit 810013
Vertex Antenna Control Unit 8100

6HU-Version of ACU 8100

4HU-Versionof ACU 8100

advantages of suggested approach
Limited scope of upgrade

computer replacement only

“budget-friendly” solution

Re-Use of components

drive cabinet, PLC and servo amplifiers



Low risk

the working interlock system and low level control will be re-used

return to existing system can easily be achieved

use of well proven components

limited software effort

Limited software effort

PLC software

can be re-used to large extent

various functions not used any more

Servo computer software

functionality already existing

only adaptations required for Arecibo (interfaces, specific interlocks etc.)

Limited telescope downtime

Estimated total downtime approx. 2-3 weeks

With a little more effort, it would even be possible to return to operation every night

Advantages of Suggested Approach
possibilities for future upgrades
Fully Digital Drive System

very flexible control loop structure

improved performance

much easier to be tuned than analog DCS

insensitive to EMI etc.

less components …less failures

… more software

measurement of commands to servo amplifiers is difficult and requires analyzers or test outputs in the computer (even more software…)

Adaptation to new host computer(s)

Extended operating modes

Drive cabinet or servo amplifiers only

Motors ?

Possibilities for Future Upgrades
fully digital drive system
Fully Digital Drive System
  • Position and velocity loops closed in servo computer
  • Servo computer provides torque command to each motor via local bus
  • In low level control the servo amplifiers receive analog commands
  • Configuration of servo amplifiers is controlled by PLC via digital inputs to amplifiers
  • Existing drive motors could be kept
  • Servo amplifiers (or entire drive cabinet) needs to be replaced
  • Analog DCS could
    • … be kept for low level control
    • … be removed, leading to a much simpler but “less comfortable” drive concept in low level control