[Larken]

G59, What resolution is the encoder and what is the max rpm you would run on the spindle ?

[G59]

BEI, 500 ppr x 2500 RPM maximum motor speed. So 20883 pulses per second at 2500rpm.
Technically a 250 ppr encoder would also do.

[Larken]

I got it working and it works good.

Here is a video running a servo with a pulley on it running with a AMC drive.

https://www.youtube.com/watch?v=6yHG...ature=youtu.be

(excuse my voice, i sound like Stewie from Family guy, lol , it was late and i was excited)

I'm cycling the motor with the Exercise mode withing the drive.
The KP was set to 1000 with KP set to 300. You can see when i change the KD to 400, it gets unstable until i change it back to 1000

I have more to finish before releasing the drive, but i have a cnc router to finish and ship in the next week, so it won't be long after that to send them out.

Larry

[G59]

Looks promising.

[ech2o2]

Hi Larry,
Would it work open loop or you think that the pwm "translation" to +/-10V will not be precise enough? You mentioned very little backlash to none...from your experience, what will be the magic number? If I need to change my encoders, would you recommend staying with linear encoders or switch to rotary? Do you have a good supplier to suggest for encoders? Thanks
Eric

[Larken]

Hi Larry,
Would it work open loop or you think that the pwm "translation" to +/-10V will not be precise enough? You mentioned very little backlash to none...from your experience, what will be the magic number? If I need to change my encoders, would you recommend staying with linear encoders or switch to rotary? Do you have a good supplier to suggest for encoders? Thanks
Eric

Eric, you have to run closed loop with an encoder, open loop would be totally useless. The USDIGITAL E5 or E6 series is the best one to get for the money. be sure to get differential outputs, and usually 1000 line is good.

The Step2Lin will be ready to ship at the end of the week . So i will send you a message about shipping.

One thing i added was a input to sense that there is power at the amplifier. It needed this to be safe, because if you turned the amp power off while the system was holding, then moved the motor, when you turned to power to the amp back on the motor would jump back violently since the encoder was still keeping the position.
So i have a opto-isolated input that will take up to 10 volts. You can just use a voltage divider off your main power that puts out 10 volts @ about 5 ma. Then when the step2lin sees the main power go off and come back on, it clears the encoder count and does a soft pwm startup.

On all my new boards, i've switched from the older 18F2331 to a 16bit DSPIC. My new PID loop is a bit improved from the older one, and i now have the Ki working much better. The sampling time is variable from 500-4000 samples per second with the Ki fixed at 1000. This makes the Ki not get unstable at high sampling rates and much more useful.

Larry

[Larken]

I'm adding some setup commands to the firmware to let you setup the analog amps easier. You will be able to set the DAC to output a test voltage so you can adjust the gain pot on the analog drive. I'm doing tests on different motors and voltages and see if the amp gain is too high, then the Step2lin barely uses the resolution of the DAC to control the motor, its better to use more resolution and have the amp gain less.
Certain higher sampling times seem to make more audible noise in the motor, so im trying different opamp bandwidth changes to suppress some of this. When the switching freq of the amp is only 20khz, high sampling times can modulate out as noise.

[ech2o2]

Hello again,
I found some information on my linear encoders. Do you think those will be compatible with your card? Thanks.

[Al_The_Man]

Those appear to be Heidenhain style which are typically 11µa sine wave, I'm guessing you will need the typical 5v square wave type. unless you can find a way to square them up, Heidenhain make add on units that will do this.
Al.

[Larken]

It looks like the scale should be useable, but you will need a little comparator and driver circuit down at the linear scale. Since the step2lin has a 4x decoder, we can try it first by just squaring up the basic resolution. Here is a little circuit that should (might) work.

I'm not sure what those photosensors output, (maybe Al knows) but i'm assuming that if you put a 1K resistor in series, you should see the 7-16 uA peak-peak appear across it as a voltage. The LM393 comparator neg inputs go to an adjustable pot to let you find the center voltage of the peak-peak swing. The 1meg resistor is optional and works to create a "snapover" hysterisis to reduce jitter at the center point. The 26C32 is a differential line driver to drive the twisted pair cable (which i highly recommend on any encoder)

You can make the circuit on a small perfboard (go to addison electronics in montreal ) The circuit should be connected down close to the linear scale and is powered by the +5volts at the step2lin down the cable.

Larry

EDIT: I forgot to add a 1K pullup resistor on the output of each 393. (They are open collector)

[ech2o2]

Thanks! That looks relatively simple and I think I already have some 393 at home!
I also found this on internet. The circuit is interesting since it amplifies the signal too. The 4069 hex inverter I found at Digikey has 14 pins and 6 comparators...so one chip. I was thinking of building two of them to generate A & B signals and maybe a third one for the index signal. I have no clue if this would work or not but it is relatively easy and cheap to try...What do you think?

[Larken]

Eric, i don't think that circuit is for encoders scales at all. It requires a fair amount of voltage from the incoming circuit, because thats where it gets its power. (the scale puts out a tiny voltage)
And Its AC coupled so it couldn't work with very low speeds, and also there is no differential output. (seriously, don't waste your time building it )

Larry

[ech2o2]

Hello! Thanks for the input! You are right about the Heidenhain scale putting out very little amps...11uA. I ll get started on your suggestion and keep you updated. Thanks again!
Eric

[daniellyall]

have a look at TI web site they have a program on there call web bench it for doing circuits they have a encoder bit on it so you can work out what's required for a circuit to run a encoder

[ech2o2]

Hi
Congratulations! I noticed on Viperservo.com that your step2linear cards were ready. I ordered 3 of them! I will let you know how it turns out! Thanks for all the help. Eric

[Larken]

All Boards have been shipped. I will have the PDF ready in a few days.

[Al_The_Man]

Larry, do you have any kind of manual put together yet?
Al.

[Larken]

Here is the manual with connection diagrams and powersupply. Its not yet finished, and but i will finish it soon. At least this should let you hook it up.
The current version of Vipertune will work with it, but i will upload a new version in a few days.

To download the manual, right click the View Manual link and hit Save Link_as
Step2Linear, ViperServo

Larry

[ech2o2]

Hello,
Here are some questions following my very first try...
1-Can a usb to serial converter be used to communicate with the step2linear card via vipertune?
2-I have 15.4V at the step2linear card and it is giving me a 3beep error: low voltage input? is that normal? or is it because i did not use the low voltage to the drive option?
3-I think there is an error on the diagram for the power supply suggested in the manual. The polarity of the condenser should be reverse since the common is higher potential than the negative out of the bridge rectifier.
4-I quickly get a encoder trip alarm. It' s not clear to me how the step2linear reacts...does it stop working until the error is corrected or it will keep working anyway and it just warning you of a problem? If the card "stops working" how do we externally reset without powering it off?
5- My drive has only one input called UREF and a common, it is not clear to me how I can use the separate plus / minus signal coming from the step2linear card? Do you have an idea?
5- In the same idea, can I assume that the the small circuit you suggested to square up my sine waves from my Heidenhain linear encoders is working since i did not get a encoder fail warning? I do not have an oscilloscope and I am not sure how to verify if my circuit really works...

Thanks
Eric

[Larken]

Hello,
Here are some questions following my very first try...
1-Can a usb to serial converter be used to communicate with the step2linear card via vipertune?
2-I have 15.4V at the step2linear card and it is giving me a 3beep error: low voltage input? is that normal? or is it because i did not use the low voltage to the drive option?
3-I think there is an error on the diagram for the power supply suggested in the manual. The polarity of the condenser should be reverse since the common is higher potential than the negative out of the bridge rectifier.
4-I quickly get a encoder trip alarm. It' s not clear to me how the step2linear reacts...does it stop working until the error is corrected or it will keep working anyway and it just warning you of a problem? If the card "stops working" how do we externally reset without powering it off?
5- My drive has only one input called UREF and a common, it is not clear to me how I can use the separate plus / minus signal coming from the step2linear card? Do you have an idea?
5- In the same idea, can I assume that the the small circuit you suggested to square up my sine waves from my Heidenhain linear encoders is working since i did not get a encoder fail warning? I do not have an oscilloscope and I am not sure how to verify if my circuit really works...

Thanks
Eric

1) Yes a USB to Serial converter does work. the ones that come with a disk allow you to set the baudrate.
2) Its the lowvoltage input that triggers the alarm. (It doesn't read its own powersupply voltage)
3) yes you are right, i'll fix that.
4)you need to get the vipertune working to be able to see if the encoder is working. Bringing the "lowvoltage" to zero will reset the step2lin.
5)Either of the analog Refouts has a full +10 to -10 volt swing. One is just the inverted version of the other to drive a differential amp input.
6)Once you get vipertune connected, you will be able to whether you can read the encoder. You can also run it as single ended if you pull down the unused input with a 2K res.

Ive attached a basic connection circuit. Here you can just connect the lowvoltage inputs to the powersupply. (Use the 2pin connector for this since you can disconnect it to reset the drive.) You don't have to connect the current sense inputs as they are only used to display current in vipertune.