Step Frequency on Old UHU Controller

[jlobin]

I'm new to the UHU, and for that matter, to servo controllers. Programs like Mach 3 talk about 25K pps drive rates. In testing my new UHU build, I can't seem to get beyond 10K without lots of overruns. The step response seems to be OK, I just can't drive it as fast as I think I should be able to. Any advice?

[H.O]

Hi,
I have no experience with the original UHU design, only with the HP-UHU. I've found that ~130kHz is about max what my setup can handle. The docs on the UHU chip is a little vague, in one place it says 100-150kz and in other places it syas it possible to reach 300kHz "depending on settings". I've found the first statement, 100-150kHz to be right on the money - with the Multiplier setting set to 0.

With that being said I had major problems at the get go with the differential interface on the HP-UHU, does the original design have that as well - ie the SN75115 integrated circuit for the differential encoder interface? If it has, try removing the two caps connected to pins 4 and 12 of the SN75115 and see what happens.

/Henrik.

[jlobin]

Henrik, thank you for your response. The original UHU does not have onboard differential line drivers, but I did test it with add on ICs. The documentation says that any overruns are bad, so I pretty much stopped testing when I started to get those at about 10K pps on the Step input.
Jack

[H.O]

Yeah, if/when you get an overrun the drive does no longer know for sure where the motor is. It can "guess" but in the end you have to see it as if you've lost position :-(

I don't know for sure if the chip keeps track of the encoder even after the following error has been tripped but you could try spinning the motor with a cordless drill or something without the motor powersupply turned on. That way the switching noice from the powerstage won't affect the circuit so perhaps you could figure out at least if THAT is the problem.

How about shielding of the encoder cable? Motor cable? Any link to the schematic and PCB files?

As I said, I've had my share of problems but none have been realted to the the CPU or its firmware.

[jlobin]

Thanks for the tip with the drill, I'll give that a try.
Jack