Messages

21

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: September 07, 2017, 03:33:22 AM »

Did away with the L298 driver and designed a simple switch based on a MOSFET. Due to the extremely low resistance of the transistor it doesn't heat at all. So the heating problem is solved. Getting 100Hz is not a problem and it works very well.

Dan

22

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: July 04, 2017, 11:55:21 AM »

Jan,

Thanks for explaining. My configuration is different. See attached photo. The magnets are between the lever and the base. The lever is suspended and balanced with the magnets at both ends. The electromagnet is stationary and pulls the lever at one end. There is an iron piece on the lever at that end. The setup works fine with the 2ohm coil, has sufficient power and amplitude up to 100Hz.

The problem is the heating. Today wound a new coil (the one on the picture), 14 ohm. but it is less powerful now and so the amplitude drops as it gets to higher frequencies. I think it has to do with the inductance. Modern stepper motors have typical resistance of the coils around 2 ohm, thus keeping the inductance low and allowing for higher speeds. The drivers limit the current so the motors don't heat up to much.

Dan

23

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: July 03, 2017, 04:26:39 PM »

Oh, that is very small current.

24

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: July 03, 2017, 10:08:45 AM »

Hi Jan,

Built a new head with a lever and magnets, but was not able to drive it fast. Only then I did away with the 24VDC commercial solenoid (around 130 ohm) and wound my own solenoid having 2 ohm. With this one I can easily do 50 and 100 HZ. But to get reliable 100HZ at full lever amplitude (around 1mm), I have to use 70% duty cycle.

Anyway, the L298 can't limit the current. I am using a 12 VDC 2A power supply, so in a minute it gets VERY hot! As well as the solenoid. It appears that a fan helps to some extent. Do you also encounter these heat dissipation issues?

Dan

25

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 11, 2017, 12:41:36 AM »

Thanks Jan. Will construct a new one and update how it worked out.

Dan

26

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 10, 2017, 03:58:41 PM »

Hi Jan,

OK. I think I now see the main mechanical difference between my construction and yours. You have a lever, while I have a plunger. Along the whole way you've been talking about your lever, but somehow I was ignoring it.

So I think if made as a lever supported by ball bearings, a spring could work just as well as magnets.

Thanks,
Dan

27

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 10, 2017, 07:05:13 AM »

The coloured engraving came out real nice.

The stroke of my plunger is around 0.6-0.8mm

So you have a fixed frequency and you only control the impact force by varying the voltage?

Where did you get your coils from? Or did you wind them yourself? I used a 12V solenoid (around 25 ohm -> 0.5A) which I made a new housing an plunger for where I can mount the tips. The spring force is around 500g.

My main concern when making the new plunger and housing was to minimize the wobble of the plunger inside the sleeve, because I was afraid any wobble could play a significant role in ruining high resolution super fine engravings. So my plunger is not too lose and hence has some minor resistance moving.

Dan

28

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 09, 2017, 02:46:00 PM »

300Hz!!!!!!!? WOW! So your mechanics using the magnets is MUCH superior to mine using a spring. Still interesting why does the L298 gives me a much lower frequency than the other driver. By the way, a nice feature of the other driver is that I can limit the current and set an idle current.

Why in your design you move the solenoid instead of the magnets? You need then fatigue resistant wire so that it doesn't break. It could be very helpful if you could post a simple sketch of your impact head mechanics. You have described it in this thread previously, but afraid I was picturing it differently than what I am understanding now.

So you have a board converting PWM to frequency?

Dan

29

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 09, 2017, 11:29:59 AM »

From your code - you only have two states for the PWM - S0 and S1000? It is not continuously adjustable within a range?

The LM298 driver didn't work for me - only was able to get about 15-20Hz max with it. With a higher end driver set to full step I am able to get 80Hz. Don't know what is the reason for that.

Dan

30

Mach SDK plugin questions and answers. / Re: Impact engraving plugin

« on: June 09, 2017, 09:50:24 AM »

Hi Jan,

Don't quite understand. Let me ask you another question: Do you have your plunger moving at a varying frequency which is dictated by the "Sxx" command? If so what is the board you're using to convert the PWM into frequency? What is the frequency range of your solenoid?

What I did is, I used an Arduino and wrote a program which reads the Z pulses and based on the Z position sets the frequency of the solenoid 0-50Hz. The I use the PicEngrave software to output rotary curving Gcode (as if you wanted to curve 3D in wood) and run this code.

I still don't understand how if commanded S0, it keeps the plunger in the upper position? It driver must complete a full cycle in order to return to the upper positoin.

By the way, I tried to output Gcode, but as I said it only had 2 "S" commands - one at the beginning and one at the end.

Dan