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Worm INDEX PULSE Generation

Hardware is now available from AWR Technology to provide an INDEX PULSE from your worm axle with one pulse being generated per revolution. This provides an absolute reference for periodic error correcting software, so once trained, it will always be right. There are two components (as shown in the photo below) a bush - like a top hat - with a slot cut in and a slotted opto-coupler. The bush shown is bored for a 12mm diameter shaft and should be glued onto the slow motion shaft. The opto-coupler needs to be held rigid so that the disc rotates through the slot. There should be part of the worm bracket nearby to which it can be glued to. Finally a cover must be made to protect the components and the leadout wire should be secured to the fixed part to stop damage to the circuits by the wire being pulled. The other end of the cable fits into the Advanced Microstep drive box into the INDEX connector.

After the end of a slew the IH works out where the telescope is in the index cycle and recommences periodic error corrections. Exact synchronism is reached at the next index pulse. The IH display shows if the periodic error corrections are active.

Jaw sizes 3.1mm and 16.7mm


Testing of the unit is performed by using a computer connected to the HOST socket in the Intelligent Handset. With the complete system powered up (Drivebox and Intelligent Handset), the IH is put into AWR mode of communications (FACTORY - COMMS). Run a terminal programme such as Hyperterminal. As soon as this programme has been set up correctly the IH will report "HOST CONNECT". You can then rotate the slotted disc and there will be a set of characters reported ":P#". This occurs every time the slot in the disc passes through the opto-coupler. If the telescope is operated at slew speed then the protocol is inhibited as the slot can go too fast through the aperture and there is not enough time to report the pulses. So do the testing at slow speeds.

The electrical circuit looks like:

INDEX HARDWARE . . . . (SMALL GAP) 33.00 (incl VAT)
Specify SHAFT diameter.
(Maximum outside diameter of slotted top hat is 25mm).

In many cases with existing equipment it will be very difficult to add the slotted disc as in the above photograph. An alternative method is to have a vane that rotates. This can be attached easily to the rotating component. This must pass through the jaws of the opto coupler at some point in its rotation. The pulse generated becomes the other way up but as the pulse detection is on an edge it does not matter to the electronics which way up it is. So the SAME LEAD can be used.

To supply just the oopto-coupler and the lead (NEW DESIGN) - SMALL GAP 15, LARGE GAP 20

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March 2003 AWR Technology