Bridgeport Series II Interact 2 Conversion

Hello all,
I'm starting my conversion of Bridgeport S2I2 Mill with a Heidenhain TNC 145C controller. This machine uses resolvers on the servo's rather than digital encoders. Within the TNC 145C there is a board that provides the A-D conversion. Not being an electrical engineer I don't think I have enough skills/tools to reverse engineer that circuit board to use the A-D function. Though I know others have with TNC 151 controllers and I find that nothing short of amazing.

By tools I mean scope and benchtop power supply, etc. I wonder if I should pick these up to help the conversion along.

So as I start the process my first question is: Is there any machine performance difference between using the existing resolvers and a Mesa 5i33 / 7i49 boards or switching them out to quad encoders and using something like a 5i20 / 7i33 combo.

There is an existing MPG that also plugs into the A-D board - I imagine it will also be a resolver type - not sure yet.


Thanks

Jay

The mill is simliar to Igor's and John's ( machineability.com/Bridgeport_series_II.html ).

The servo's have both a resolver to provide angular position feedback just like a digital shaft encoder - and a tach for velocity feedback to the drives. The resolvers are sin/cosine based rather that A quad B style. I think the sin/cosine style are called resolvers (?). My schematic for the machine shows both the encoder aka resolver circuit to the control, and the tach circuit to the drives.

There are no glass scales.

I didn't want to strip it completely out like Igor did, but take a less invasive approach much like John's - only I don't have his skill in re-using the TNC analoge-to-digital converter board.

Jay

what are the model number of the "resolvers' (are they heidenhain)
Heidenhain often used analog sine waves to produce digital TTL.
Your MPG's are most likely analog sine waves.
If this is true, then you can buy the conversion boxes on ebay (EXE 650)

A resolver is a rotary transformer where coupling between windings varies as the
winding is turned. It is a totally passive device, just wire and laminated iron, no
electronics. Heidenhain used analog encoders, both rotary and linear for many
years, most of them with current outputs. These are NOT resolvers, and a resolver
converter or reader will not accept the signals. If the resolution is high enough,
the signals can be converted to digital with a simple comparator circuit. The current
output can be converted to voltage with a resistor. The outputs of these analog
encoders are sine/cosine signals, and can be interpolated to increase resolution.
Also, if these encoders have light bulbs in them, you should either replace the
entire unit with something more modern, or at least replace the bulb with an IR
LED. Replacing the whole encoder has the advantage that you can increase resolution at the
same time. Replacing linear encoders is more expensive, rotary encoders
are relatively cheap today.

Jon

They are Hendenhain ERO 115 125 D12. I've taken one apart and it has a copper disk with slots in it around the circumference - so I suppose the term Analog Encoder would then be what it is. I'm borrowing a scope from a friend in a week or two and will be able to see the signals at that time. My alternate approach is to try and re-use the existing A-D Board. The Heidenhain manual calls it the Analog Component Board. Encoders and handwheel feed into it, and supposedly digital signals come out. Again the scope will help me determine that.

So given that they are Analog Encoders, I'm now not sure if the resolver boards from Mesa of Pico would work with it. If that's the case then my choices narrow down to:

A. Try to re-use the Analog Component Board like John did with his conversion
B. Replace the Analog Encoders with Digital Encoders

From John's Web page where he documented his build

For the initial setup I just used halrun with a test hal file. This way I could test to see that the motors moved according to the command signal and check the position encoder feedback. This was the first setback in the project as I found that the Heidenhain encoders produced analog sine and cosine 125 cycle/revolution output signals. So to handle the encoder output problem I took the encoder interface board from the old Heidenhain controller and mounted it on the back of the cabinet door close to the PC. The Heidenhain board then outputs 625 A quad B digital cycles per revolution giving a resolution of 2500 counts per revolution. The ball screws have a 5mm pitch and are driven by a 2:1 timing belt reduction from the motors. So 2500 counts of the encoder represents 2.5 mm of motion or .001mm per count.

Jay