Robotic ObsVermes

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Reference

See the link list.

Dome

Overview

Original door drive
Original azimuth drive with IR control.

The dome is 2.6m in diameter and constructed as a glass-fiber reinforced polyester doubleshelled sandwich structure, thermal isolated with rigid expanded plastic core from Baader Planetarium.

The dome has a rollover shutter which originally was actuated by a hand crank.

The dome has a friction wheel drive for the azimut motion. The friction wheel is driven by a worm gear motor "Danfoss Bauer GmbH, Esslingen, 75W, 19.5tpm, 18.7Nm, 1:70 gear reduction, type BS 02-38H/E04LA4C1". The motor was operated as single phase condensor motor and controlled by an infrared remote control.

Dome Azimuth Control

Test setup of the barcode reader dome azimuth position detection system

We modified the motor for three phase operation and control it by a frequency inverter which in turn is controlled via RS232 serial interface from a computer. The frequency inverter is a 650V (650V/002/230/F/00/DISP/RSO) from SSD Drive.

For azimuth position feedback we installed a system based on two standard CCD barcode readers mounted in a defined spacing reading barcodes mounted to a strip around the inner circumference of the dome. With this setup one hundred codes would give a better than a one degree precision.

Dome Door Control

Door drive with motor added
Conductor rail to bring electrical power to the moving dome after full assembly. There is about a 1 cm distance between the motor and the tap.

We mounted the same motor which is used for the azimuth drive. The shutter drive is controlled by a frequency inverter which in turn is controlled via RS232 serial interface from a computer in the same way as the azimut drive.

Additionally there is a control system based on an embedded controller Alix 3c which connects to end position switches via Toradex isolated 8 channel digital input unit and offers an INDI based interface.

To be able to power the motor which opens the door, the mounting of a conductor rail was needed. The conductor rail including a collector unit was delivered by Paul Vahle GmbH + Co. KG.

Control information and other data is transferred to the moving dome via WLAN.

Drawing of door drive gear

Telescope

The dome synchronized with the middle of the slit (red dot).

The mathematical background and a solution of the telescope dome slit synchronization was developed by Toshimi Taki. Our solution (use MathematicaPlayer to view it) for the dome slit synchronization and the telescope pier collision avoidance has been derived with Mathematica and a simulation has been carried out.

Dome slit synchronization

Since May 2007 the synchronisation is in place and the dome slit never missed the optical axis more than 4 degrees. See two examples of telescope and dome in motion.

Pier collision avoidance

The last bang: a very unusual telecope position

To avoid under any circumstances a collision between the telescope and the supporting pier a software module has been developed. Two straight lines representing the edges of the mounting plate of the telescope are used to cut the pier cylinder resulting in a simplification of the calculation without loosing the physical significance. The first tests carried out in May 2007 are very promising.

Acceleration sensor

Accelerometers with a sufficient accuracy became recently available for an affordable price. Two devices from Toradex are attached to the HA- and declination axis to achieve an independent measurement.

Guiding telescope

A careful simulation showed that off axis guiding has severe drawbacks because it introduces a motion of the guiding star relative to the center of the optical axis. The motion is an effect of the atmospheric refraction which depends on the zenith angle.

SBIG STV

The guiding is performed with a Vixen FS 102 refractor and a SBIG STV. The focusing is done with Robo-Focus.

Detector

CCD camera

The CCD camera is a Finger Lake Instrumentation (FLI) PL16803 system.

Filter wheel

The filter wheel is a FLI Precision CFW-5-7 system equipped with UBVRI and a Halpha filters.

Focuser

The focuser is a FLI PDF system.

Weather

Meteostation

Meteo Pole

Currently we have installed a Davis Vantage Pro2 meteo station mounted on a telephone pole.

The meteo station is connected via a "Cabled Weather Envoy" with an RS232 serial interface with the observatory webserver where the free Meteo software collects the data.

The latest measured values can be seen at observatory webserver. Some weather graphs are also available.

Integral cloud, precipitation and ambient light sensor

To get an overview of the cloud cover, the ambient light and the state of the precipitation we use the AAG CloudWatcher cloud detector

Narrow field cloud cover imager

Based on a thermopile sensor TPS534 by Perkin Elmer which is supplied with a infrared filter blocking shorter wavelengths than 5.5 µm a cloud cover detector will be built.

In a second step the sensor will be mounted to a cardanic scanner and an all sky cloud cover image will be produced.

Mains Power Switching

For several mains power switching task we use an IP Power 9258 ethernet power switch from Aviosys and one from KOUKAAM.

Connection to the Internet

The observatory is currently connected to the Internet via a Swisscom ADSL 3500. The DSL connection is done by a Netopia 3346 Modem/Router. As the mentioned ADSL connection is based on static IP address assignment which is redone about once per month. In addition a dynamic DNS Service DynDNS is used to keep the host accessible when IP has changed.

The connection has a an averrage upload bandwith of 24.5 kB/s.

System integration

RTS2

Initial sync of the cupola with the Astro-Physics GTO mount.

RTS2 provides operational integration of all necessary components as well as hooks for data reduction. Positional information received from data reduction can be fed back into a telescope model. It is in use at several observatories.

The two missing core components, the Astro-Physics mount and the dome (cupola) drivers, have been developped during winter 2009/2010. The cupola driver is specific to the observatory hardware while the Astro-Physics GTO mount driver is intended for general use.

INDI

The INDI WebClient displays the communication tab of the Astrophysics mount driver.
The INDI Kstars Client displays the same items as the INDIWebClient (see above).

The various above mentioned components are glued together with INDI (Instrument neutral device interface).

For the purpose of remote control INDI fits our needs perfectly. In a nut shell the advantages are:

  • It is a multi client multi server environment with the ability to distribute and chain servers and their drivers.
  • Driver development is straight forward, well it depends on the complexity of the driver functionality.
  • Existing clients provide access to the drivers via GUI without the need to program them
  • Drivers communicate with other drivers providing the possibility of a fast response to various (emergency) conditions.
  • Compound tasks can be automated using command line tools.

INDI itself and its protocol are still under development but the provided environment already permits to control our observatory remotely via the Internet.

Some notes about INDI

The INDI WebClient is currently prepared for a public release under GPL.

INDI Web Client documentation