Messages

5331

General Mach Discussion / Re: MACH3PLASMA LIMIT SWITCHES FOR G540/PROMA

« on: February 09, 2018, 02:41:36 PM »

Hi,
its common practice to wire all the limit switches in series with normally closed contacts. When any one switch operates the continuity of the switch string is broken and
that is what Mach detects. There again its common, but not universal to have Mach Estop on a limit event.

Large and powerful machines are even more safety oriented and a limit event will cause the axis drives and spindle to de-power. When a machine de-powers in such a manner
it is a time consuming matter to restart the machine, assuming no damage is done, and pick up where the job currently in the machine is and start from there.
None the less safety requires such an arrangement, if the controller has 'brain fade' and the EStop doesn't work or is slow, it is essential that the machine be made safe.
Because of the inconvenience and lost time a great deal of effort is expended to prevent a machine from ever operating the limit switches.

Mach has soft limits. They are programmed usually to be just inside the physical limits and limit switches. The program will detect that you or your Gcode is attempting
to drive your machine out of bounds and stop you. They work really well, but they absolutely rely on the machine being referenced or homed. So when you turn your
machine on and you 'home' your machine it will drive to pick up its home switches in each axis. Mach knows thereafter where it is in relation to the boundaries of the
machine and soft limits become useful.

It is for this reason that I argue that good, reliable, repeatable home switches are more important than limit switches. For about a year or so I operated my mill
without home switches and suffered a few crashes because soft limits didn't work because the machine was not repeatably referenced. Once I got around to fitting
home switches the number of out of bounds moves dropped dramatically. Good home switches were the best addition/development I ever did on my mill not to mention
very cheaply too!

Craig

5332

General Mach Discussion / Re: uc300 analog input outputs

« on: February 09, 2018, 05:38:50 AM »

Hi,
yes if the existing motors are good then new drives would certainly be the way to go.

I had not played with a decent AC servo until fairly recently when I bought a secondhand 1.8kW Allen Bradley servo and drive.
It wipes the floor with any DC servo I've come across. The tuning software has a database of electrical, thermal and physical characteristics
and even magnetic characteristics including saturation and hysteresis. All manner of control modes, pulse, analogue, all manner of modes torque, velocity
and position, indexing both speed and position, incorporates its own limit switches, able to program any number of digital and/or analogue performance
indicator outputs, programmable following error and the list goes on. I'm still learning about what they can do.

Many of the Eruopean and American brands are very expensive, as I say Delta (Tiawainese/Chinese) is a good compromise. About $1000US for a 1.5kW servo and
drive with a 20 bit absolute encoder. Makes mincemeat of DC servos.

Craig

5333

General Mach Discussion / Re: uc300 analog input outputs

« on: February 09, 2018, 05:03:49 AM »

Hi,
I priced some DC servos for a customer, spares for his aging plasma table and I was shocked at the price and for 100-200w servos at that!

Have you seriously looked at the prices of AC servos and drives. I don't think I would be going for the cheapest Chinese stuff but Delta is a very good
brand and a good compromise between price and quality.

If I'm not mistaken they'll make DC servos look like yesteryears expensive tech.

Craig

5334

General Mach Discussion / Re: uc300 analog input outputs

« on: February 09, 2018, 04:13:54 AM »

Hi,
machdrives have parallel port breakout boards and DCservo amps. Do you use or need either?

Craig

5335

General Mach Discussion / Re: mach3 randomly doesnt follow the correct toolpath

« on: February 09, 2018, 03:58:18 AM »

Hi John,

should i switch to mach 4??? instead???

the first board is a Mach3 ready USB controller, they have caused a lot of hair pulling by people over the years but they do work apparently but is absolutely worthless for
Mach4.

The second board is a straight parallel port breakout board and you could use that with the Darwin parallel port of Mach4 but the parallel port is limited, I wouldn't
recommend it, it'll be as frustrating as what you face now.

The last one is a UC100 by CNCDrive and IF ITS A GENUINE ONE its very good indeed. The reason I highlighted the comment is because there have been hundreds of
Chinese rip-off UC100s. If its one of those throw it away.

If your serious about Mach4 be prepared to buy a GOOD external controller and no Chinese s*********t. There are five manufacturers of GOOD Mach4 ready boards, the cheapest
is about $120 and the flashest one is $600. I use an ESS about $180 plus 2 x $50 for two breakout boards. The PMDX-424 is about $225 and is ready to go. PoKeys
and CNCDrive have some great products too. At this time there is no Chinese manufacturer making credible Mach4 products and if they try to tell you otherwise
walk away.

Craig

5336

General Mach Discussion / Re: Mach3, PC with standard Paralel port working, just like to confirm input speeds

« on: February 09, 2018, 03:21:17 AM »

Hi,
I think that all input signals to the motion controller are monitored, I wouldn't say sampled exactly, but are monitored by high speed circuitry. Those signal are only
very slowly reported back to Mach. Some signals like THC are handled within the controller and what gets reported back to Mach is a bit irrelevant.

THC UP and THC DOWN are not handled like ordinary signals.

Imagine you have Mach plan a move in the X and Z axes. The move is 100mm in X but because of a slight tilt on your plate the Z axis needs to lower by 1mm over the
100mm cut. Between Machs planner and your parallel port controller the controller produces 100,000 pulses to the X axis and 1000 pulses to the Z axis, I have
assumed 1000 pulse per mm to make it easy, and the move is planned to take 5 seconds. For simplicities sake we'll ignore the accel-deccel stages of the move.
The pulse rate is 100,000/5= 20kHz for the X axis and 1000/5=200Hz for the Z axis.

Once the move has been planned and dispatched to the controller it can't be changed. However WE DO NEED TO CHANGE IT ON THE FLY to accommodate THC variation.
Lets say that the THC variation is 0.5mm in addition to the 1mm the Z axis is lowering and again to make it less confusing say that it happens evenly over 100mm.
Given that Mach and the PC have planned and dispatched the move the motion controller is now the only device that can change the Z motors path. The motion controller
will insert one extra pulse every two normal pulses. So over the entire move the Z axis has lowered 1000 pulses due to the plate angle and 500 pulses due to THC.

That was a highly idealized example to show how it works. Imagine now that the THC variation is +0.5mm over the first 50mm and then -0.5mm over the last 50mm.
The controller will insert one pulse for every one normal pulse, change the direction signal at the 50mm point and insert one pulse for every normal pulse but in the
other direction. As you can see this starts to get complicated quite quickly and is happening very rapidly. There is no way you could transmit the data back to Mach and have
the main CPU do the calculation, by the time it even got the data it would be too late.

THC is a specialized function of the motion controller, it really has little to do with Mach at all.

Craig

5337

General Mach Discussion / Re: MACH3PLASMA LIMIT SWITCHES FOR G540/PROMA

« on: February 09, 2018, 02:48:23 AM »

Hi,
OK, those switches I linked to can be used as limit switches as well but are fairly sizable. The ones you pictured will work OK.

Another possibility is inductive proximity sensors, they can make for a tidy and robust installation.

No matter what switches or sensors you use you should give some thought to what happens if the axis runs away. Trust me it DOES happen!
Any switches/sensors in the way are going to get crunched, may not be the end of the world but certain arrangements or mountings mean that even
a runaway axis won't break them.

Craig

5338

General Mach Discussion / Re: uc300 analog input outputs

« on: February 09, 2018, 02:19:55 AM »

Hi comet,

Exactly proves my point,you should not have to assume anything with equipment that could potentially cause harm or damage.

I understand your concern but you have elected to go with Mach3, a DIY CNC software program and a UC300 hardware motion controller of VERY VERY modest price
and taken on the role of 'Machine Integrator' whether you actually intended on doing so or not. The risks and benefits of doing so are yours alone.

There are alternatives.......Fanuc and Siemens make state of the art controllers and software, just be prepared to pay $20,000 AND annual fees.

Craig

5339

General Mach Discussion / Re: Mach3, PC with standard Paralel port working, just like to confirm input speeds

« on: February 09, 2018, 02:00:30 AM »

Hi,
Mach3 inputs are polled at about 10Hz known as the macro pump rate.

Machs inputs are not suitable for inputs which change very quickly, THC would be one example. Another would be the index signal from a spindle, even
a lathe spindle at only 300 rpm for threading has an index pulse every 5ms. This signal is used among other things to synchronise the start of the thread.
Mach needs to respond positively in something under 1/2ms to have any chance of being accurate.

Machs normal inputs are way way to slow to be of use in those circumstances.

Those high speed/critical timing signals are handled by the motion controller.

If you use a parallel port it may not be evident that you have a motion controller but you do. The parallel port driver takes numerical information from Machs motion
planner and uses the PCs CPU to produce high speed high accuracy pulse streams to the motor drivers. All in all the parallel port driver is a very clever bit of work.
So when Mach is running there are two bits, Machs GUI /motion planner and the Parallel Port Motion Controller.

The motion controller offers high speed signal control for a number of common CNC processes, THC and Lathe threading are two, but probing, homing and axis squaring
are among others. You can't program most motion controllers so you can only do what the maker of the controller built in. You may have seen Galil, Vital Systems and
PoKeys offer motion controller level programming, usually at extra cost. This low level high speed program code could be very useful for a project which requires
high speed signal processing that is not a standard motion controller feature. You will need to be a competent programmer to make sense of it.

The de-bounce is a number supplied to the motion controller from Mach to set the number of 'time slices (40us at 25kHz)' that a signal is to be monitored before the
signal in 'known to be good'. It is a kind of filtering arrangement designed to stop very rapid transient voltage signals from falsely be interpreted as a valid signal.
The length of the time slices gets shorter as the kernel frequency goes up. Lets say you had a problem signal and had it 'heavily' debounced for 10 time slices at
25khz, ie 400us. If you then upped the kernel speed to 45kHz (22us) you need to increase the number of times slices to maintain 400us filtering 400/22=18 (about).

The simple summary is that Machs input are good for slowly varying signals, a few Hz whereas the motion controller can handle signals well into the kHz range. Debounce
is a simple filtering technique and is convenient to do programmatically as opposed to fiddling with little capacitors.

Craig

5340

General Mach Discussion / Re: MACH3PLASMA LIMIT SWITCHES FOR G540/PROMA

« on: February 09, 2018, 01:14:05 AM »

Hi,
are you looking for home switches or limit switches?

I know a lot of people combine the two jobs but there are some good reasons why that is not the best. It used to be that because we all had only parallel ports we
had to economise on inputs. With external controllers offering many more inputs you don't, in fact probably shouldn't do that today.

My recommendation for home switches are Omron or Honeywell Roller Plunger microswitches. They offer good repeatability and accuracy and can be mounted within
the machine boundaries thereby freeing the very ends of travel for the limit switches.

http://www.machsupport.com/forum/index.php/topic,36285.msg248575.html#msg248575

Craig