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USING ENCODERS
FIRST SOLUTION A PUSH-TO SYSTEM
Encoders with a BARS BOX display for large heritage telescopes

SECOND SOLUTION (BELOW)
High resolution encoders with computer connection and external display units.

THIRD SOLUTION (BELOW)
High resolution encoders with Intelligent Handset connection (low cost 10 arc second resolution).

AWR have installed a set of absolute encoders made by HEIDENHAIN on the YAPP 36 inch telescope at the Space Science Centre, Herstmonceux. This gives this elderly telescope a set of digital setting circles. The standard demonstration software supplied with the IK220 encoder card (IK220.EXE) was modified to provide an output of each channel using TCP/IP protocol and hence available over the local computer network for use by other programmes or other computers. The absolute encoders were of type ROQ425 having 8192 lines per revolution and a count of turns. Thus by gearing up the primary axis by about 20 times the overall resolution is under 10 arc seconds. The other change made to the standard installation is the lead length. We evaluated the set-up with 25 metres of cable between the encoder and the computer card. The specified limit is 10 metres. The serial interface standard is RS485 for DATA and CLOCK pairs of lines and the power supply lines were doubled up to halve the voltage drop along the cable. A further pair of wires were used as voltage sense wires, conencted at the encoder end and measurable at the computer end to check that the power supply specification for the encoder had not been violated.

The HEIDENHAIN IK220.EXE programme when set up for ENDAT absolute encoder mode does not have any offset or scale factors that can be applied to the data. Not to worry, the calibration is done in further software written by AWR Technology to convert the encoder numbers to astronomical units (HHI.EXE). We also modified the IK220.EXE programme to provide TCP/IP export of the emcoder data.

FEATURES of HHI PROGRAM

  • Reading TCP/IP data provided by the encoder card IK220
  • Translation into RA, DEC, ALT, AZ, HA, LST, UT
  • Calibration data in a .INI file.
  • Automatic fold over of the DEC coordinate when it goes over the pole.
  • Accurate time fetch from web time sources.
  • Appears as an Intelligent Telescope to a Planetarium programme running Meade LX200 generic protocols
  • Coordinate synchronisation with Planetarium programme
IK220, HHI and the Planetarium programme can all sit and run happily on the same computer or on different computers. Further, large readout display units can be fitted to request any of the seven parameters made available. Calibration can use ABSOLUTE or INCREMENTAL encoders fitted to the telescope.

RETROFITS
These encoders can be fitted to any telescope which is manually, partially driven or fully driven. They are eminently suitable for TANGENT arm and SECTOR drives but you do have to provide gears to operate the encoder over the full working angle you require. MACK CONSULTANTS and AWR TECHNOLOGY fitted this encoder to all four telescopes at the Equatorial Group, Herstmonceux (ex RGO), now the Observatory Space Science Centre:

All four now have a pair of Astro Display Units giving rreadouts of RA and DEC and plaetarium computerisation allowing objects to be retrieved quickly.

Guide prices are £2000 for the Heidenhain equipment, £300 for the AWR software and other items as needed. Design help is available from Alan Buckman at AWR at normal commercial rates.

SECOND SOLUTION using HEIDENHAIN encoders

External encoders now integrated into Intelligent Handset with extra hardware - a QUADRATURE DECODER BOX.

AWR have recently designed an interface to take signals from the TTL output version (ROQ425) HEIDENHAIN ENCODERS and convert it to pulse and direction as used in the Intelligent Handset. This means that with suitable gearing, a closed loop encoder system is now available for the IH, with enough resolution to provide very accurate positions. The converter box takes two quadrature pulse trains and converts to pulse and direction. The resolution depends on the gearing from the prime axis to the encoder and is as accurate as the mechanical gearing will allow. The main advantage is that if there is slippage in the main drive (for example if friction drive reduction is used) then it now does not matter. Separate menu functions in the IH allows setup of the encoder resultion.

This solution is on the

This product can use any quadrature output encoder including the low cost Hewlett Packard encoder sold by JMI. Further details of upgrade price on this extension product please contact AWR. It can be supplied in various configurations, so it is necessary to price it accordingly. As a guide it is from £160.00 (UK price).

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