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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:
- Extension for azimuth 4:1 gearbox shaft (near azimuth limit
switches).
- Mounting post/collar for azimuth ROC412 absolute encoder
(Heidenhein part number 257 044 01).
- 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.
- 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.
- Collar for elevation ROC412 absolute encoder which is
"piggybacked" on top of RON806. Drawing Eki&Ola,xxx.
- Elevation enclosure not required due to IP64 classification.
- Mounting the axis firmly to the encoder, loose vs. tight.xxx
At least the following critical tolerance requirements must be
verified before mounting the encoders using mechanical gauges or
something similar:
- For RON806s:
- Alignment area in mounting collar: 180mm in diameter,
tolerance "H7" meaning "larger by a maximum of 0.039mm".
- Tolerance 1: alignment area xxx 0.02mm.
- Tolerance 2: alignment area xxx 0.1mm concentric in diameter.
- Tolerance 3: collar edge xxx 0.1mm planar across the perimeter.
- Rotating shaft: 60mm in diameter, tolerance "g7" meaning
"smaller by a maximum of 0.0099mm, larger by 0.039mm".
- Tolerance 4: surface accuracy of the shaft extension 0.02mm.
See figure xx. dimesions in mm/inches.
- For ROC412s:
- Movement in axial direction (towards or away from the
encoder): max 0.5mm.
- Axial misaligment (rotational centers of both shafts do not
align): max 0.5mm.
- Angular misalignment of shafts: max 1 degree.
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:
- 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.)
- 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.
- A RS232-mux/switchbox required for testing the controlling system before
final installation. Will be connected next to control
room RS232 to RS422 converter.
- A two-channel D/A output card ET-1728 (FIM 1433) plus its
adapter card ETD-7285 (FIM 215); we already have them.
- 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:
- An EC-1120 enclosure (FIM 1891); we already have one for
motor rack PC.
- A CISA-486H CPU card (FIM 1761).
- An AMD486DX4-100---120 processor (about FIM 500).
- A heat sink without fan for the processor.
- A 16MB SIMM RAM memory module (about FIM 650).
- A floppy disk drive (about FIM 200).
- 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).
- 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.
- A temporary keyboard; we already have it.
- An IK121 Heidenhain RON806 interface card; we already have
two of them.
- An ET-1722B digital I/O card (FIM 919) for absolute ROC412
encoders.
- Interface card for converting ROC412 open cable end to 50-pin
ribbon cable connectors. (An ETD-781 (FIM 379) will most probably do.)
- 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.
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.
Main tasks of the control room PC:
- Read the latest VAX commanded azimuth and elevation.
- Send a request for Heidenhain RON806 encoder readouts to
tower PC via 115kbaud serial link.
- Get readouts via the same serial link.
- Compute and output error signal via D/A to ESSCO analog
servo, taking simulated panel offsets into account.
- Display readouts on VGA screen.
- Repeat over.
Main tasks of the tower PC:
- Wait for a serial request for Heidenhain RON806 encoders.
- When a request arrives, read the values from IK121 and send them
down via 115kbaud serial link.
- 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:
- Read absolute position.
- Set error signal D/A output so that antenna moves to go over
both index marks.
- When index marks have been found, initialize IK121 to
predetermined offsets (==absolute value assumed to be at index marks).
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:
- 220V for PC.
- 220V for RS232/RS422 converter.
- Two pairs of twisted-pair cable from converter to downstairs.
- One pair from PC reset switch to downstairs!
- IK121: two D9-terminated cables to RON806 encoders.
- 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.
- 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?).
- Temporary keyboard and VGA monitor connections.
Allready removed!
This means measuring that the tolerances described in
tolerances have been met. A few interesting limitations:
- 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?)
- Moving the antenna to rotate shafts will lose the position in
which the antenna was "left" when Inductosyns were removed.
At the moment the intention is to mount ROC412 on top of RON806 to the
elevation shaft.
1mdeg > 1mV...
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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