The Pm-1440gt Has Landed

[Ischgl99]

I took the factory controls out and added a PLC for the controls on my 1236T. The nice part with that is you can easily change the program if you want to do something different instead of rewiring relays or a circuit. Another advantage is you can add an operator interface panel to add more functionality of you desired. I already had an older micro PLC and the programming software from my consulting days, so it cost nothing to do.

I built a proximity stop, but already had tooling to thread away from the chuck. I do both methods and haven't decided which I prefer yet. I do mostly metric and need to keep the half nuts engaged, so both methods work well for me. Threading away from the chuck is even easier with imperial, you can position a hard stop where you want to start, move the carriage to that point and then engage the half nuts to start threading.

To help avoid crashing the tooling with the proximity stop while threading, I programed the PLC to latch the enable bit when the stop is reached, and require using reverse to unlatch it, so that way I can't accidently feed into the work when reseting the proxy stop. I can also use that when threading metric away from the chuck, use the proximity stop to position the tool where you want, then only reverse is enabled and you can't thread the wrong way accidently.

 

[Beantown]

I took the factory controls out and added a PLC for the controls on my 1236T. The nice part with that is you can easily change the program if you want to do something different instead of rewiring relays or a circuit. Another advantage is you can add an operator interface panel to add more functionality of you desired. I already had an older micro PLC and the programming software from my consulting days, so it cost nothing to do.

I built a proximity stop, but already had tooling to thread away from the chuck. I do both methods and haven't decided which I prefer yet. I do mostly metric and need to keep the half nuts engaged, so both methods work well for me. Threading away from the chuck is even easier with imperial, you can position a hard stop where you want to start, move the carriage to that point and then engage the half nuts to start threading.

To help avoid crashing the tooling with the proximity stop while threading, I programed the PLC to latch the enable bit when the stop is reached, and require using reverse to unlatch it, so that way I can't accidently feed into the work when reseting the proxy stop. I can also use that when threading metric away from the chuck, use the proximity stop to position the tool where you want, then only reverse is enabled and you can't thread the wrong way accidently.

Interesting! Kind of overkill, but right up my alley! I haven't messed with a PLC in 20 years. I'll have to look into that option as well. I bet your electronics cabinet it clean! If you wouldn't mind PMing me a picture that would be awesome.

 

[vvanders]

There's some pretty neat PLC solutions out there these days. Automation Direct has a couple PLC lines(Click, Productivity) that are pretty reasonable cost-wise while having quite a few features.

I built a full PID loop based solar water pump a while back with some of them and was pretty straightforward for someone who hasn't worked with PLCs in any sort of professional capacity.

 

[Ischgl99]

Definitely overkill for what these machines need, but ease of making changes and adding features is definitely nice to have. I used an Allen-Bradley Micrologix, I would never spend the money on a new one for something like this, but as vvanders mentioned above, Automation Direct has some nice PLCs that are not that much more than the relays you would need to purchase if you went with the prox stop, so price wise, it makes sense. I don’t think I would have done the prox stop if I didn’t have the PLC controlling the lathe, I didn’t have much room in the small panel at the machine to add more relays, and the PLC made adding that simple.

 

[B2]

Hi @Beantown

Did you use a microprocessor or discrete logic ICs? Solid state relay or transistors? If you have any pictures or a schematic you would be willing to share that would be awesome. I wanted to do a microprocessor, but after reading about how noisey VFDs were I didn't think it would be very reliable. ICs should be much less sensitive.

I am sorry if I was not clear.

If you click on the link I provided you will see the details of my solid state conversion for my PM1440GT. Here it is again, just click on my user name, "B2 said:" , where the yellow up arrow is located and it will take you to the thread:

VFD conversion using solid state electronic components.

The VFD has all of the control logic that is needed, with the possible exception of the safety latch for maintaining a signal to the VFD. There is vircually nohthing that you could do with a microprocessor or with logic ICs, besides most machine controls like to run at 24Vdc. You will see in my circuit drawings that I used old fashion cheap discrete bi-polar transistors that cost less than $0.10 each. I think I used a total of 7or 8 of them for all of the circuit plus all of the extra features that I added, like having an auto/manual oiler pump control. With my design, and physical layout, I have never seen a noise problem of any kind. The safety latch is simply two transistors, Q2 and Q3. You can use the big multi-contact relays, but my guess is that the coil switching currents and mechanical contacts create a lot of the noise issues that everyone talks about. Any noise issues are associated with what voltage/current spikes reaching the VFD control inputs and so inductive coupled currents that get onto the lines going to the VFD control inputs are a potential problem. I threw in a bunch of color LEDs into my design to aid in debugging any potential circuit failures and in a couple of places they are used to provide bias voltages to enable better turning on or off other transistors so any mechanical switch etc have a high impedance. Anyway, go to the link above and pick up the attached document called: "PM 1440GT Part 2 VFDDescription ..." . In this are drawings, descriptions, as well as parts lists. There is even an TOC lines which are linked to locations in the document. In the end, I don't think there is a lot of functionality differences between the solid state conversion and the relay conversion as most of the logic control/lifting is done by the VFD. After this, the only differences are the extra features and physical size of the relays. I got every thing into the two PM1440GT cavities, the one at the back of the stand where the original electronics were located and the small one at the front panel of the lathe where the front knobs are located. The relay version does not leave much space in the back and so the VFD and the e-braking resistor has to be located elsewhere, either in and external box or in the lathe stand cavity on the end just under the change gears etc. Hence, more wires must come in an out to go to and from the VFD etc. This may add to the relay version having more noise issues. To activate the VFD control inputs one simply sources a couple of milli-amps of current into the VFD input connection. Cut off the current and this de-activates the VFD. So this is easily done with a bi-polar transistor or even a mechanical switch.
While my circuit drawing is in the above mentioned documentation as well as at that thread I will post it again, here, to make it easy for you to see.

The transistors, Q2 and Q3 are the heart of the safety controls and form the safety latch. As long as current is flowing through one of them it holds the other one in the on position. So this feedback causes the pair to be latched on. If the current is discontinued then they do not conduct again until a separate source turns one of them on. In this case, current injected at the base of Q3. One sets the latch by initially providing current at the base of Q3 via R8 and the neutral position of the run mechanical switch, so that current can then flow through these transistors. Current cannot flow if any of the series connected mechanical switches shown above the latch, such as the e-stop, are not conducting. Proximity sensor Q1, and the associated Red LED, is provided because some proximity sensors have some internal impedance, hence they may have a voltage drop across their outputs even when turned ON. Q4 and Q5 are used to turn the lathe motor on in forward or reverse directions when the forward and reverse switches are turned on. In concept they are not needed but by using them and connecting them to the latched safety circuit so that the lathe input cannot be put to the run condition if the latch has not be set. Q6 and Q7, via diodes D1 and D2, are used with the oil pump so that the pump can run when the lathe is turning. The diodes between the jog inputs and the forward and reverse inputs are to prevent the forward and reverse run signals from causing a jog signal, the other colored diodes in this area are simply to allow the user to see and so know which lines are active. If you have any questions about any part of the circuit just let me know.

If you prefer not to respond to my curiosity I understand. I see you are located in Idaho. But to me, Beantown usually means Boston? How did you choose Beantown as a user name?


Dave L.

 

[Beantown]

Hi @Beantown

I am sorry if I was not clear.

If you click on the link I provided you will see the details of my solid state conversion for my PM1440GT. Here it is again, just click on my user name, "B2 said:" , where the yellow up arrow is located and it will take you to the thread:

The VFD has all of the control logic that is needed, with the possible exception of the safety latch for maintaining a signal to the VFD. There is vircually nohthing that you could do with a microprocessor or with logic ICs, besides most machine controls like to run at 24Vdc. You will see in my circuit drawings that I used old fashion cheap discrete bi-polar transistors that cost less than $0.10 each. I think I used a total of 7or 8 of them for all of the circuit plus all of the extra features that I added, like having an auto/manual oiler pump control. With my design, and physical layout, I have never seen a noise problem of any kind. The safety latch is simply two transistors, Q2 and Q3. You can use the big multi-contact relays, but my guess is that the coil switching currents and mechanical contacts create a lot of the noise issues that everyone talks about. Any noise issues are associated with what voltage/current spikes reaching the VFD control inputs and so inductive coupled currents that get onto the lines going to the VFD control inputs are a potential problem. I threw in a bunch of color LEDs into my design to aid in debugging any potential circuit failures and in a couple of places they are used to provide bias voltages to enable better turning on or off other transistors so any mechanical switch etc have a high impedance. Anyway, go to the link above and pick up the attached document called: "PM 1440GT Part 2 VFDDescription ..." . In this are drawings, descriptions, as well as parts lists. There is even an TOC lines which are linked to locations in the document. In the end, I don't think there is a lot of functionality differences between the solid state conversion and the relay conversion as most of the logic control/lifting is done by the VFD. After this, the only differences are the extra features and physical size of the relays. I got every thing into the two PM1440GT cavities, the one at the back of the stand where the original electronics were located and the small one at the front panel of the lathe where the front knobs are located. The relay version does not leave much space in the back and so the VFD and the e-braking resistor has to be located elsewhere, either in and external box or in the lathe stand cavity on the end just under the change gears etc. Hence, more wires must come in an out to go to and from the VFD etc. This may add to the relay version having more noise issues. To activate the VFD control inputs one simply sources a couple of milli-amps of current into the VFD input connection. Cut off the current and this de-activates the VFD. So this is easily done with a bi-polar transistor or even a mechanical switch.
While my circuit drawing is in the above mentioned documentation as well as at that thread I will post it again, here, to make it easy for you to see.

The transistors, Q2 and Q3 are the heart of the safety controls and form the safety latch. As long as current is flowing through one of them it holds the other one in the on position. So this feedback causes the pair to be latched on. If the current is discontinued then they do not conduct again until a separate source turns one of them on. In this case, current injected at the base of Q3. One sets the latch by initially providing current at the base of Q3 via R8 and the neutral position of the run mechanical switch, so that current can then flow through these transistors. Current cannot flow if any of the series connected mechanical switches shown above the latch, such as the e-stop, are not conducting. Proximity sensor Q1, and the associated Red LED, is provided because some proximity sensors have some internal impedance, hence they may have a voltage drop across their outputs even when turned ON. Q4 and Q5 are used to turn the lathe motor on in forward or reverse directions when the forward and reverse switches are turned on. In concept they are not needed but by using them and connecting them to the latched safety circuit so that the lathe input cannot be put to the run condition if the latch has not be set. Q6 and Q7, via diodes D1 and D2, are used with the oil pump so that the pump can run when the lathe is turning. The diodes between the jog inputs and the forward and reverse inputs are to prevent the forward and reverse run signals from causing a jog signal, the other colored diodes in this area are simply to allow the user to see and so know which lines are active. If you have any questions about any part of the circuit just let me know.

If you prefer not to respond to my curiosity I understand. I see you are located in Idaho. But to me, Beantown usually means Boston? How did you choose Beantown as a user name?


Dave L.

Awesome. Thank you for the information. You were clear! I just didn't notice that the one quote took me to your thread! Still learning the ins and outs of this forum features. I will give this all a good read through.