DRO Switch

[redpiperbob]

Hi All
I have a mill with a 3 axis dro setup on it  and a lathe with 3 axis dro each uses Allandale scales.
I have only one display unit what I would like is an electronic switch that would allow me to switch between the two different inputs. can anybody help with a circiut.
Thanks in advance Bob

[kwackers]

Little bit of guesswork here - but what I'd do:-

There are 2 outputs from each scale for the quadrature signal and a 5v line to power the scale. The quadrature outputs are at logic levels (0 - 5v).

For a pair of scales take the 'A' quadrature lines and run each of them through a diode (cathode first), join the anodes and then connect via (say) a 10k resistor to the base of any common NPN transistor. The emitter of the transistor should be connected to ground and the collector is the output 'A' signal and should also be pulled to the 5v line via say a 4k7 resistor.

Do this for the remaining 2 'A' lines and the 3 'B' lines.

Then group the 5v power lines for the lathe and the 5v power lines for the mill. To switch between scales simply use a SPDT switch to set power to one set of scales or the other.
This'll work because you're using a simple wired 'OR' for the A and B signals, with no power the output of the scale will always be low allowing the powered scale to drive the transistor.
The transistor will invert the output but this won't matter since both A & B will be inverted and the signals are symmetrical.

Bear in mind the unit won't know that you've changed from one to the other, so it won't 'remember' position etc.

You can also do the same with logic chips, but this is simple can be built on strip board and costs buttons.

Parts:
6 * NPN general purpose transisters
6 * 10k res
6 * 4k7 res
12 * IN4148 or similar diodes
1 * SPDT (or DPDT) throw switch
Connectors to suit

If you can't visualise the circuit let me know and I'll try and find something to draw it with...

[andyf]

Being a simple soul. I'd be tempted to use mechanical rather than electronic switching, with a separate Lorlin type 3 pole rotary switch for each axis, and click all three over to change the display from one machine to the other. If I were feeling particularly ingenious, crank arms on the switch shafts and a con rod would allow all three to be switched in unison.

Andy

[kwackers]

One of the problems with mechanical switching is 'bounce'. Each time you flick the switch you'll get contact bounce which the console will interpret as movement.

I've never been a big fan of complex mechanical switches, invariably at some point one or more of the contacts becomes noisy which is bad for this sort of application.

If however a multipole switch is the way you fancy, you can get 'ganged' switches. Just need one with 6 poles of SPDT, lots of rotary switches can do that.

[DMIOM]

One of the problems with mechanical switching is 'bounce'. Each time you flick the switch you'll get contact bounce which the console will interpret as movement.

I've never been a big fan of complex mechanical switches, invariably at some point one or more of the contacts becomes noisy which is bad for this sort of application.

If however a multipole switch is the way you fancy, you can get 'ganged' switches. Just need one with 6 poles of SPDT, lots of rotary switches can do that.

Would second all that Kwackers says, the only things I would add are (a) make sure the switches are all break-before-make, and (b) add at least one extra pole to switch the power, as I'm not sure if the display would be up to driving two full sets of scales concurrently.

As an additional observation, the setup for a Mill display can be different to that for a Lathe; so if, for example, you had the display in diameter mode when using the lathe, there is a risk you might then read double the distance traversed when using it on the lathe.....

Dave

[Davo J]

I have the instructions from the guy at Meister DRO's for a switch to switch the quill and knee scale over. I will chase then up tomorrow for you. I am sure he said you can do it with only 2 wires from each and a switch to suit.

Dave

 

[Bluechip]

Apart from the 5V power stuff ..

Could the ( 74HCF ) 4051, 4052, 4053 not be used for this sort of thing ... ?

Used them a fair bit for signal jiggery-pokery .. unless the circuit won't tolerate the 150-odd ohm insertion ..

Dave BC

[kwackers]

I have the instructions from the guy at Meister DRO's for a switch to switch the quill and knee scale over. I will chase then up tomorrow for you. I am sure he said you can do it with only 2 wires from each and a switch to suit.

Dave

 

You can, they're the A and B quadrature lines. Trouble is with 3 axis you need six poles on your switch (or a separate 2 pole switch per axis).

[redpiperbob]

Hi All
All sorted I have a circuit draw by a member of another site. Just putting the bits into a box.two 74HC157N's two resistors and a capacitor and a switch.



Hi Steve you get on this site too I have just finished making the board for the rotary table indexer (CNC site) and I am awaiting the programmer from Hong Kong.

Thanks for all your suggestions
Bob

[Davo J]

I hope I am not butting in here, but Bob has said he has solved his problem.

Since you seem to be up on electronics, you might be able to help me out if you can.
I have been looking around for years for a way to join the quill and knee scale together into one axis of the 3 axis readout. I did contact Meister about it and they only suggested a switch as I wrote above. The lathe DRO I have combines the 2 Z's together internally so it can be done.
I have seen on practical machinist a while back where a guy bought a box from Acu-Rite that did this but at a cost of $500 US and just lately another member contacted them and they are making one up for him, so they can be made up.
Do you have any suggestion? They are all TTL signal scales and read outs, I haven't tried anything incase I blow something up. which could end up expensive

Dave

I have the instructions from the guy at Meister DRO's for a switch to switch the quill and knee scale over. I will chase then up tomorrow for you. I am sure he said you can do it with only 2 wires from each and a switch to suit.

Dave

 

You can, they're the A and B quadrature lines. Trouble is with 3 axis you need six poles on your switch (or a separate 2 pole switch per axis).

[kwackers]

@DavoJ The switch simply swaps between the two - is that what you want? i.e when the switch is in the quill position the knee can be moved without changing the readout. If this is the case any of ideas above will work, although given it's only two scales you can probably just use DPDT throw switch.

If you want to sum the two axis then the best way is probably using a micro controller, this will read movement on both scales simultaneously and output a new quadrature signal. It's a fairly simple tax and a very simple circuit but it does require some programming knowledge.

[kwackers]

Hi Steve you get on this site too I have just finished making the board for the rotary table indexer (CNC site) and I am awaiting the programmer from Hong Kong.

Thanks for all your suggestions
Bob

I knew your username was familiar - just wasn't sure why.   

[Davo J]

Yes it is the summing of the two I am after, I know how to go the other way about it.

Dave

[DMIOM]

......I have been looking around for years for a way to join the quill and knee scale together into one axis of the 3 axis readout......

Yes it is the summing of the two I am after, I know how to go the other way about it.

Dave,

I have used the "ESUM" from US Digital for exactly this purpose (albeit on a machine where I had fitted two of US Digital's own encoders) - but, as you say, if the signals are standard, it ought to work for you as well

cheers / Dave (IOM)