What Features Should A Machine Control System Have?

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Mad Monty

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I'm developing a machine control system (for a mill, lathe, drill press, etc.) and have started a list of features that I thought could be useful. I'm looking for feedback on which you think would be useful, useless, or better if somehow modified - and what I've left out. Write as much or as little as you like - but please write something if you possibly can because I really need the input if the result will be useful to anyone.

Rather than cluttering the thread with individual thanks, I'll tell you in advance that I appreciate any and all responders and will send back to them a summary with my findings. When the design work is done, I'll share that as well.

The list:
  1. safe start-up (protection against accidental start-up)
  2. continuously variable speed
  3. high low speed torque
  4. RPM readout
  5. reversibility
  6. limit switches at end of travel
  7. foot switch control
  8. status indicator lights
  9. electrical, temperature, and mechanical overload protection
  10. instant emergency stop
  11. soft start-up (controlled acceleration)
  12. torque or stiffness control, that is, you can make it stiff so it chews through tough material without bogging down, or soft, so it slows or stops when the going gets tough and you want to limit the torque (say to protect your tooling, like tapping a hole).
 
Seems like overkill for a drill press, but I suppose those that use it for perhaps tapping would find it useful
A control for a lathe, another for a mill sounds good. (one to do both would have to be either too expensive, or too limited IMHO) You've covered everything I can think of, (short of built in CNC) I'm afraid I can't contribute anything new.
Thanks for the idea and the ability to do this.
 
That about covers it. That would be sweet. That's a list one often thinks would be nice to do, however knowhow & knowledge is not up to the task.
When can we expect the first prototype? :grin:
We've got plenty of equipment over here to try it out on...
 
T Bredehoft said:
Seems like overkill for a drill press, but I suppose those that use it for perhaps tapping would find it useful
A control for a lathe, another for a mill sounds good. (one to do both would have to be either too expensive, or too limited IMHO) You've covered everything I can think of, (short of built in CNC) I'm afraid I can't contribute anything new.
Thanks for the idea and the ability to do this.
Click to expand...

If he was talking about a drill-press a simple foot switch would meet most of his requirements.
 
With the exception of #5, all the rest are covered by installing a VFD. Lets not over think this. As far as all the indicator lights, are you going to watch the lights or the work in progress? Full voltage indicators suffer from lack of maintenance, lamp life is extremely short. The Xfmr and LED type are very expensive. Lights are generally used when the work in progress can not be observed.
 
Number 6, limit switches. You need what I would call DEADMAN switches. If something were to happen to the operator all power feeds would stop instantly. On the lathes some of the different owners have posted their modifications to their machines.

Mills need them on the table feeds, need two sets. One is permanently mounted near the end of thread of the lead screw. the other is movable.

One short coming is if the switch(s) is/are stuck in the "Stop" position the machine will not run. Chasing down a switch in the "Stop" position can be frustrating. You have a good list
 
I will be interested to see what you come up with. If you can keep the cost low enough it will be a winner.:encourage:
 
Everything on your list has existed in one form or another for the last 100 years, if you can bring the cost down to "free" many people will be interested.
Good Luck with that.

Solving a more serious problem with machine tools would be eliminating the inertia inherent in rotary or linear motion systems, look into it (no pun intended)
 
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For a lathe:
variable speed, reversible spindle with digital rpm readout
CSS (Constant Surface Speed which controls spindle rpm as a function of crosslide position)
constant torque mode
overload protection (your over torque/current spec)
variable/reversible feed screw who's rate is tied to spindle rotation (feed screw servo controlled and tied to spindle rpm eliminates secondary transmission)
electronic threading (for multi screw lathes where threading screw is servo controlled and tied to spindle rpm and reversible)
electronic spindle braking
configurable limit switches that can stop motion and spindle.

(good example of the above would be a Hardinge HLV-H)

For a mill:
variable and reversible spindle speed with digital rpm readout
constant torque mode
constant speed mode
overload protection
servo or stepper power feed (without eliminating manual control) on at least the long axis, optionally tied to spindle rpm for controlling tool loading during cuts
configurable limit switches that can stop motion and spindle
electronic spindle braking

So where do I send my deposit? :D

I've had similar thoughts over the years. Are you attempting just the control system and leaving the drives/motor modifications to the machine owners? In my thinking about something like this I would prefer to change the machine over to a BLDC spindle motor and (ideally) servo motors for the various drive systems. BLDC is more efficient and the control logic/software has many of your desired features built in. And it is potentially easier to tie everything together this way. I've had my eye on those spindle motor/control systems at automation technology for some time now and will eventually do something like this to my PM25. I actually started writing code a ways back to do the electronic lathe but I don't remember where it is, or if I even have it anymore. Too little time, too many ideas...

And before anyone makes the inevitable comment about why not just getting a cnc machine, I don't want nor need a cnc. But a little help with some things would be useful. And I can't afford a HLV-H...:)
 
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I like the auto threading idea, essentially a a motion control system that would have positional analysis in all real dimensions.

As others have pointed out, a VFD pretty much does all the motor control functions in a robust format, and one can customize/program the configuration to the specific application. You need just basic functions for mechanical machining, but want the built in safety features, that make up for your momentary lapses. Add a few control relays, switches and logic diodes and you can do what you have outlined for a reasonable cost. This is what I have on my lathe (with idiot lights, so I know why the machine stopped). I have been building a few low voltage control boards for others, and they pretty much does what Monty has outlined for both the lathe and the mill. My mill uses a factory BLDC with variable speed, and uses induction sensors to give true speed and also to control the motor speed/direction for tapping. The table feed uses VFD technology with limit stops that just interrupt the direction signal. A dead man foot switch, is just an E-Stop on the floor, or one can wire it to a foot brake. I have been using double redundancy systems for my control systems and stops. Call me paranoid, but it has saved my skin more than once.

My thought would be more toward the future of having a unified full wireless (or some simple digital daisy chain type wiring) control system for these machines, this would allow all levels of control from straight mechanical use with DRO function/travel control stops to full CNC. Flat touch panel would allow all forms of screens/programmability that might interface with your VFD or BLDC, in a simpler fashion. All axises would be motorized and have position sensor information driven off magnetic scales or some form of encoder system that is hard reference to the axis, so you do not need travel limit switches, etc. The set-up screen would prevent over-driving any axis, and if needed limits due to a fixture that would would be kept in memory, along with tooling parameters. Some form of inexpensive wireless smart sensor to do positional analysis and integrate into the central controller. Some form of material feed and speed calculator built into the system, maybe smart chip technology on the tool holders that will dictate the calculations (not unlike CNC software). Some form of auto-alignment for tooling based on the sensor in a quick chuck system. So not far off from what a Tormach mill does with an easier interface, wireless controls and less expensive. The cost of technology like this has come way down in price, but the question is there a market and the investment to do so without spending a fortune. Certainly when you look at how far robotics has come in many different technology, hopefully the trickle down effect will come into the hobbyist affordability range at some point.

When it comes down to it, at our level, the machines haven't changed much (with maybe the exception of VFD and more affordable CNC) for the last century. With the exception of Tormach machines, or self built systems, I haven't really seen much change in what is available.
 
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