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2. Suggested steps

2.1 Draw sketches of mechanical fittings

These sketches will allow rough estimates of the number of fitting pieces that need to be manufactured, their complexity level, and possible difficulties that can be expected. The fittings include at least:

  1. Extension for azimuth 4:1 gearbox shaft (near azimuth limit switches).
  2. Mounting post/collar for azimuth ROC412 absolute encoder (Heidenhein part number 257 044 01).
  3. Collars for matching RON806 to Inductosyn locations. Two collars are identically made at machinery company Mekapo Oy. The desing of the collars based on old Inductosyn encoder mounting and the needs of the new Heidenhein encoders, which dimensions are smaller than the old ones used to be. Drawing Eki&Ola,xxx.
  4. Extension heads for both azimuth and elevation shafts, diameter 60mm. Elevation shaft head requires a further extension 6mm in diameter for absolute ROC412 and its K17 coupling. Drawing Eki&Ola,xxx.
  5. Collar for elevation ROC412 absolute encoder which is "piggybacked" on top of RON806. Drawing Eki&Ola,xxx.
  6. Elevation enclosure not required due to IP64 classification.
  7. Mounting the axis firmly to the encoder, loose vs. tight.xxx

2.2 Devise a plan for verifying encoder mounting post tolerances

At least the following critical tolerance requirements must be verified before mounting the encoders using mechanical gauges or something similar:

For RON806s:

  1. Alignment area in mounting collar: 180mm in diameter, tolerance "H7" meaning "larger by a maximum of 0.039mm".
  2. Tolerance 1: alignment area xxx 0.02mm.
  3. Tolerance 2: alignment area xxx 0.1mm concentric in diameter.
  4. Tolerance 3: collar edge xxx 0.1mm planar across the perimeter.
  5. Rotating shaft: 60mm in diameter, tolerance "g7" meaning "smaller by a maximum of 0.0099mm, larger by 0.039mm".
  6. Tolerance 4: surface accuracy of the shaft extension 0.02mm.

See figure xx. dimesions in mm/inches.

For ROC412s:

  1. Movement in axial direction (towards or away from the encoder): max 0.5mm.
  2. Axial misaligment (rotational centers of both shafts do not align): max 0.5mm.
  3. Angular misalignment of shafts: max 1 degree.

2.3 Purchase the pair of control room---tower PCs and cards

The control room PC should be a rack-mounted model similar to the existing VLBI control PC. It will eventually run Linux-based antenna control programs and take care of antenna status monitor display, located in control room rack. Apart from the standard PC equipment the following should be added:

  1. A RS232 to RS422 converter to ensure down-up 115kbaud link reliablity. (Most probably COM-1485 by Capax (FIM 463) will do, if it is fast enough.)
  2. An interface to accept coordinates from VAX parallel output. The wire-wrapped prototype by Jouko will be able to do this. The final VAX interface electronics is also being designed and may be substituted. A new ribbon cable may be required. An old VAX or new PWM card is required for FET-card testing.
  3. A RS232-mux/switchbox required for testing the controlling system before final installation. Will be connected next to control room RS232 to RS422 converter.
  4. A two-channel D/A output card ET-1728 (FIM 1433) plus its adapter card ETD-7285 (FIM 215); we already have them.
  5. Interface cable from the D/A card to ESSCO servo rack. We already have the MIL-type connector and any shielded cable will do.

The tower PC will be similar to the final motor rack PC: an industrial enclosure with a set of ISA-based cards. (This "extra" PC will eventually act as a "live" backup spare.) The following equipment will be needed:

  1. An EC-1120 enclosure (FIM 1891); we already have one for motor rack PC.
  2. A CISA-486H CPU card (FIM 1761).
  3. An AMD486DX4-100---120 processor (about FIM 500).
  4. A heat sink without fan for the processor.
  5. A 16MB SIMM RAM memory module (about FIM 650).
  6. A floppy disk drive (about FIM 200).
  7. An 3.5" IDE hard disk drive. We will use some extra drive we already have---capacity is not critical. In the final version the hard disk will be replaced by a non-volatile solid-state flash EEPROM disk such as PC-FD-10 10MB flash disk card (FIM 2337).
  8. A temporary VGA card plus a temporary VGA monitor. The possibility of buying a small monochrome VGA display such as the 9" FT-7112 (FIM 997) will be considered---it would be nicer to handle in tower.
  9. A temporary keyboard; we already have it.
  10. An IK121 Heidenhain RON806 interface card; we already have two of them.
  11. An ET-1722B digital I/O card (FIM 919) for absolute ROC412 encoders.
  12. Interface card for converting ROC412 open cable end to 50-pin ribbon cable connectors. (An ETD-781 (FIM 379) will most probably do.)
  13. A 16-channel 16-bit A/D converter card such as ET-2816 (FIM 2863) which will read the tiltmeter outputs and a few temperature sensors inside and outside the PC. Adapter card ETD-8125 (FIM 441) plus a D37 cable (ET-10137-1, 1m, shielded, FIM 113) has screw terminals for tiltmeter open ended cable.

2.4 Connect RON806s to IK121 card in current test PC

This step is to verify the operation of software supplied with IK121 and to calibrate away the effects of cabling etc from sinusoidal signals, according to Heidenhain manuals.

2.5 Write two DOS programs: one for control room PC, one for tower PC

Main tasks of the control room PC:

  1. Read the latest VAX commanded azimuth and elevation.
  2. Send a request for Heidenhain RON806 encoder readouts to tower PC via 115kbaud serial link.
  3. Get readouts via the same serial link.
  4. Compute and output error signal via D/A to ESSCO analog servo, taking simulated panel offsets into account.
  5. Display readouts on VGA screen.
  6. Repeat over.

Main tasks of the tower PC:

  1. Wait for a serial request for Heidenhain RON806 encoders.
  2. When a request arrives, read the values from IK121 and send them down via 115kbaud serial link.
  3. In the meantime, read all encoder values, all tiltmeter values, all temperature values, and log them to a text file on hard disk.

The existing manual control panel ("standby, manual, velocity, aux") will remain operational: if VAX is not requesting new coordinates, the pair of PCs will still read out the encoders and display the values on downstairs VGA screen.

The tower PC must also be able to search the index position of incremental encoders by using the absolute ROC412 encoders:

  1. Read absolute position.
  2. Set error signal D/A output so that antenna moves to go over both index marks.
  3. When index marks have been found, initialize IK121 to predetermined offsets (==absolute value assumed to be at index marks).

2.6 Connect control room PC to VAX and analog servo

2.7 Arrange a temporary place for tower PC

The PC will most probably occupy the same space as the final motor control rack. Despite the PC is in a "industrial" enclosure it may be necessary to put it in a temperature-controlled box. (There are no major "heaters" inside the PC unlike in the final motor rack.) A supplier of ready-made enclosures could be found.

Even though the setup should be temporary there will still be at least two external screw terminal boards outside the PC enclosure, one for tiltmeter A/D connection and the other for ROC412 absolute encoders. The PC will require standard 220V (as will the RS232/RS422 converter...) and the following cables will be connected:

  1. 220V for PC.
  2. 220V for RS232/RS422 converter.
  3. Two pairs of twisted-pair cable from converter to downstairs.
  4. One pair from PC reset switch to downstairs!
  5. IK121: two D9-terminated cables to RON806 encoders.
  6. Digital I/O: 1 or 2 50-pin ribbon cables to screw terminal board to which open ends of ROC412 cable will be terminated. ROC412s can steal their +5V power from 50-pin connectors.
  7. A/D: D37 shielded cable to screw terminal board to which open ends of the tiltmeter and a set of LM34 temperature sensors will be connected. LM34s will get their power from xxx (PC +/- 12V?).
  8. Temporary keyboard and VGA monitor connections.

2.8 Arrange RS422+reset connections (three twisted pairs)

2.9 Mount the tiltmeter

2.10 Mount azimuth ROC412 absolute encoder

2.11 Remove old Inductosyn encoders

Allready removed!

2.12 Design, document, and manufacture fittings for encoders

2.13 Install and verify performance of fittings (without encoders)

This means measuring that the tolerances described in tolerances have been met. A few interesting limitations:

  1. It is slightly problematic to move the antenna without encoders of any kind. Tolerances must be verified before mounting new encoders. (Perhaps azimuth absolute ROC412 is in place and a temporary mounting post for elevation ROC412 can be made?)
  2. Moving the antenna to rotate shafts will lose the position in which the antenna was "left" when Inductosyns were removed.

2.14 Install both RON806s and elevation ROC412

At the moment the intention is to mount ROC412 on top of RON806 to the elevation shaft.

2.15 Recover approximate absolute position of antenna

2.16 Fine-tune (in software) offset and gain of difference signal

1mdeg > 1mV...

2.17 Check pointing

Large linear offsets will be found by searching the edge of Sun. Standard pointing checks will be performed using either/both continuum five point or/and 22GHz line five point measurements.


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