PWM for Brake Control

[Lyrical_CT]

Design Improvement Ideas :

I currently use a 24v DC slipping brake (either Clarke or Warner) to prevent a reel of film from over-rotating -

With Previous motion controllers - i have used timers at first then progressed to using a Virtual axis and a switch to make my pulse from NX- Digital output card to a Solid State Relay  (PSWITCH command for anyone familiar with TrioBasic) and this has worked pretty well.

I have the same physical setup on a new piece of machinery but am now using NJ and Sysmac -

Have used a TOF and TON in inline ST to control brake and it sort off works - brake can feel a bit lumpy and can chatter and bounce a bit adn am worried about the reliability when the machine is running and the controller is doing more.

(brake cycle time t#10ms and tried at 100ms also)

I did try using the Time Proportional Out FB - but this was far worse than the above.

I think i will try my luck at created a new virtual axis e.g.

Rotary Mode - min 0 max 1000

Run with MC_Move_Velocity when Machine is running and use an MC_digital Cam Switch to create my output Pulse.

I am new to the Forum and trying to get more involved with others rather than working in Isolation - so wondering if anyone has any suggestions or thoughts  or have done anything similar in SS?

Thanks in Advance,

[Lyrical_CT]

Well MC_DigitalCamSwitch does not look like the way to go - think i will  just stick with the ST code above - with my brake cycle time at T#5ms - it seems okay for now.

[ahbest]

You wrote you're using a brake cycle time of 10 ms. If you use an NJ controller your cycle time will be 1 ms. So also the timer functions will have a 1 ms accuracy. It means you calculate a percentage, but in reality it goes up and down by 10% (1ms is 10% of 10 ms).

If you want to have it more accurate, you could for instance program it with a 0,1 ms interrrupt routine. With a counter that runs from 1 to 100 you will still have a 10 ms base time, but the output can be controlled with a 1% accuracy.

At the init of the counter set on the output (immediate refresh). When the counter reaches the set percentage, turn off your output.

 

[Lyrical_CT]

Thanks for your suggestion - i will look into this and see if it makes a noticeable difference - i understand what your saying just not sure how to implement it -

Most of my work with the NJ as been with using Cams - so i'm not too sure on how to program a 0.1ms interrupt routine?

Can you point me in the right direction?