Messages

4801

General Mach Discussion / Re: Setting new cnc router build to achieve max servo speed

« on: April 14, 2018, 02:32:46 PM »

Hi,

Here is how i am doing the calculations 3200rpm ÷ 60sec ÷ 2 gear ratio x 500 encoder cpr = 53000Hz

Close but don't divide by 2 for the gear reduction. If the encoder is monted on the ballscrew it would be correct but you want to put the encoder on the servo, the shaft
for it and the mounting holes are already provided.

So if you are convinced that you want to run it at 3200 rpm it will require a pulse stream of 106 kHz. I see the CNCDrive servo drives have a rather crude electronic gearing
mechanism which could be used to bring the pulse rate required to comfortably within the UC300 capabilities.

The bottom line is that the hardware you have proposed will work. Is it the best combination for the money?

For instance:
The Keling servo is rated at 7.8A continuous with a torque constant of 0.1895 Nm/A thus rated torque is 7.8 x 0.1895=1.478Nm.
At 3000 rpm which is (3000/60)X 2 XPI=314.15 radian/sec for rated power output of 314.15 X1.478 = 463 W.

You could therefore expect a 400W AC servo to perform very siimilary to the DC servo you have proposed which would be cheaper than the DC servos.

Alternately you could go for a 750W AC servo such as the link above and the extra torque would mean you don't have to have any gear/belt reduction
for a traverse speed of 30m/minute for very similar money.

Brushed DC servos are old school stuff, AC servos are the current and have been for 15 years.

Craig

4802

General Mach Discussion / Re: Setting new cnc router build to achieve max servo speed

« on: April 14, 2018, 06:42:25 AM »

Hi,

which is in range of Mach3 frequency output

If you are using a UC300 then Mach doesn't produce pulses at all, it produces numeric data (Position/Velocity over Time) to the UC300 and the UC300 produces the pulses.
If memory serves the UC300 can handle 100kHz.

500ppr encoders are 2000 count per rev. At 50 rev per second or 300rpm that is 2000 X50=100kHz

With the servos I got the pulses from the encoders should result to 53KHz

Don't know how you calculated that.

I am still of the opinion that AC servos would be superior.

https://www.automationtechnologiesinc.com/products-page/ac-servo-motors/dmm-dyn4-servo-kit-750w-w-nema-34-frame/
From the same supplier, greater power, much expanded control options including electronic gearing. Note that you don't need a power supply, just hook up 230VAC and your ready to go.
If you compare costs (DC servo plus encoder plus drive plus power supply) then the AC servos start looking like good value and once you realize the flexibility that AC servos have....

Craig

4803

General Mach Discussion / Re: Can you wire a proximity sensor directly to a motion control board like a pokeys

« on: April 14, 2018, 02:37:59 AM »

Hi,
that diagram that Roaster has come up with is exactly what I mean. There is a path from the supply of the prox sensor (12V) through a diode, a 10K resistor through the 2 ohm resistor to the
57CNC. You don't want to apply 12V to the 57CNC input, it will handle 5.5V max.

In the first pic you have the sensor represented as a plain open collector transistor, no problems, the series resistor and Zener diode are not required.
The second pic the sensor is depicted as an open collector transistor with a pull-up resistor R2. This is close to what Roaster has posted. The series resistor R1 and the Zener diode are now
required otherwise the supply of the proximity sensor has a path to the 57CNC. The Zener will ensure that the pin is not subjected to greater than 4.7V.
The last picture is an alternative. It requires a diode only, it will prevent the supply voltage via R2 getting into the 57NC.

Crai

4804

Mach4 General Discussion / Re: MPG strange behavior

« on: April 14, 2018, 01:33:40 AM »

Hi,
yeah that would be cool.

Craig

4805

Mach4 General Discussion / Re: MPG strange behavior

« on: April 14, 2018, 12:47:26 AM »

Hi Chad,
just wondering how you do this, I've put functions in the PLC script before and just about made the log unusable as a result.

Just take out your messages, otherwise it will put the message into the log thousands and thousands of times, and then put your two functions right into the PLC script. 

Craig

4806

General Mach Discussion / Re: Can you wire a proximity sensor directly to a motion control board like a pokeys

« on: April 14, 2018, 12:37:30 AM »

Hi,
that link nor any that I googled really explain for sure what the output circuit of the sensor looks like.

If it just the collector of a transistor with its base controlled by the sensor there is no oppurtuiny for it to source any current and would be safe to hook direct to th 57CNC.
If for whatever reason the manufacturer put a pull up resistor or even a very low current leakage path from the 12V supply to the prox sensor to the output that voltage could
reverse bias the input of the 57CNC MCU and blow it up.

Do you want to risk it?
If you don't you'll need a resistor and a Zener diode.

Craig

4807

Mach4 General Discussion / Re: MPG strange behavior

« on: April 13, 2018, 11:44:11 PM »

Hi,
I think what Chad means is you put the function calls in the PLC script so they get repeated but the function definitions can stay in the screen load script. All functions in the screen load script are available to be called from
any where in the GUI.

As you have written it the function AxisSelect() gets called only when ISIG_INPUT10 through ISIG_INPUT13 are changed as monitored by the signal library. Chad reccommendes that they be called at every pass
of the PLC script. In fact you could delete ISIG_INPUT10 thru ISIG_INPUT13 from the signal library, the PLC will run dozens of times per second so having the input signals monitored is somewhat redundant.

Chad also mentions taking out the messages so the log does not becomes dominated by endless repetitions of  confirmation of AxisSelect() function calls. I'm just not quite sure how he means to do that...
if your still listening Chad I'd like to know how you do that.

Craig

4808

General Mach Discussion / Re: Can you wire a proximity sensor directly to a motion control board like a pokeys

« on: April 13, 2018, 11:15:26 PM »

Hi,
section 3.2 page 18 of the manual shows the representative circuit diagram of a DI5P input pin.

My concern is that if your proximity sensor assumes a voltage greater than 5.5V it will be transferred via the LPF to the MCU of the controller. DON"T let that happen or you'll fry it!

Presumably the proximity senor is just an open collector outut in which case any supply voltage of the sensor cannot leak back into the 57CNC. If however there is anything resembling
a pull-up resistor in the proximity sensor that voltage will get back into the 57CNC with unpredictable results. I'm imagine you'd be rather annoyed if it transpired that a proximity sensor
had damaged your controller. I would recommend a current limit resistor and Zener diode to be safe.

Craig

4809

General Mach Discussion / Re: Licensed version, will increasing kernal speed prevent missed charge pump pulses

« on: April 13, 2018, 06:28:53 PM »

Hi,
as Bryanna has pointed out mach3 Demo is limited to a kernel speed of 25kHz. The good news is that your PC will do a better job at 25KHz than it will at a higher speed.

Back when I used Mach3 and a parallel port I would from time to time experiment with increasing the kernel speed. Everything about Mach got worse as I did so. The ONLY time
you would increase the kernel speed is if you need Mach to produce pulses really fast to accommodate a servo with a high count encoder or your are trying to read a highspeed
MPG or encoder.

The bottom line is...don't bother. If you need high speed pulse streams or need to read a highspeed encoder/MPG get yourself an external motion controller like a SmoothStepper, it
will read/generate pulses up to 4Mhz, 160 times faster the Machs parallel port!

As far as a charge pump goes, I don't use one and have not bothered with one for five years without problems. They were supposed to turn the machine off (power input) if the PC stopped
talking to Mach, it doesn't happen that much, if at all. Likewise there is a feature called a 'watchdog timer' in Mach left over from caveman days that no one uses any more either.

There are many more interesting a productive things you could be doing with Mach than trying to get the charge pump to work perfectly.

Craig

4810

General Mach Discussion / Re: Setting new cnc router build to achieve max servo speed

« on: April 13, 2018, 06:08:59 PM »

Hi,
I'm going to assume that the Voltage Feedback constant is a misprint, it should be 18.95V per 1000 rpm.

That would require an open circuit voltage of 57V, much more reasonable and sensible. Probably worth an email to the manufacturer to confirm before spending
all that money.

As to how fast Mach can drive such a servo will depend on what encoder you use.

If you use a 500ppr encoder for 2000 count per rev then at 3000 rpm or 50 rev per second Mach would need to produce a 100kHz pulse stream. Machs parallel port
just wont go that fast. An external motion controller like a SmoothStepper will do it easily.

The situation gets even worse with higher resolution encoders, say a 2500ppr or 10000 count encoder will require 500kHz pulses, well into differential signaling with something like
a SmoothStepper.

You may have noticed that all AC servo drivers have 'electronic gearing'. It consists of a clever bit of computing that allow you to specify 'how many encoder counts are advanced per input pulse'.
It is done by you programming two numbers, a numerator and a denominator. For example:

1000 (Mach input pulse) X (250 (numerator)/ 5 (denominator) )= 50,000 (encoder counts)

Thus you can use a relatively slow input pulse stream like Machs parallel port to produce highspeed motion with high resolution encoders as commonly fitted on servos. This extra computing facility
is built into the servo drive and allows great flexibility when using AC servos. I'm not aware of any DC servo drives that have the same facility.

Craig