Spindle speed control

Hi,

I realise the last post to this topic is almost exactly a year old, but I am having the same sort of issue.

I am controlling the spindle speed on my machine with a variable frequency converter which uses 0 - 10 V to control the speed. The CW and CCW signals control the direction. I have built a simple PWM - voltage converter to generate the control voltage. Essentially it all works fine and the speed and direction can be controlled using S(peed) and M3, M4 and M5 commands.

If I set the 'pwmgen.0.offset' value to 0 it all works fine and the speed is the same in both CW and CCW directions. However if there is an offset the speeds are different in the two directions. To get the machine spindle speeds to match the command speeds I need to have some offset because of non linearity somewhere in the system, particularly at low speed.

Having looked at the PWM output it is clear that the the duty cycle is different in CW and CCW directions for the same set speed if the offset is not zero.

I am now at something of a loss at how to progress. I don't really understand why the PWM is not the same when the commanded speed is the same value.

I have looked around the HAL manual and it is not very helpful with regard to how the offset works. I would really appreciate some help with this or ideas about where to go next..

Thanks

Don

Andy,

Thanks for the prompt reply.

It did occur to me that might be the way it worked. So effectively if the spindle speed is, say, 200 rpm to high CW it reduces it by 200 to get the correct speed. If you are going in reverse CCW it effectively increases the rpm as it regards the CCW rpm as negative.

In the HAL manual it suggests for Output type 1 that if you need positive PWM for both CW and CCW to use the 'abs' component to convert the PWM signal to always be a positive value. I am not sure quite what the implications of this are in terms of the CW and CCW signals. My HAL coding skills are pretty negligible at the moment so I cannot easily try it. Might this be a solution?

I could have a spindle encoder input. Is there a function that allows this to be used to control the spindle speed or would I have to write one?

Don

Andy,

Again thanks for the reply. I agree that the ' motion.spindle-speed-out-abs' HAL pin is the way to go.

However, this is not loaded in my configuration, only the motion.spindle-speed-out and motion.spindle-speed-out-rps are available. I have tried loading the abs function without success.

How to I make the motion.spindle-speed-out-abs pin available?

As I said I am something of a novice regarding HAL so apologies if this is a foolish question.

Don

Andy,

That seems to have cracked it. Have upgraded to 2.6.8 and I now have the pins. A quick check using the motion.spindle-speed-out-abs pin seems to provide the same DAC output in both directions. I will now need to calibrate it to get the right speeds.

Many thanks for your patience and help.

Don