Power Drawbar Safety Mechanism

[RJS100]

I recently completed a CNC conversion of a PM833TV. So far all is good!!!

I am thinking of making a small upgrade to the power drawbar. Currently there is a crude mechanical mechanism that activates a microswitch which kills power to the spindle when the drawbar is activated. While this provides the desired safety, it is cumbersome to slide this mechanism back and forth every time you wish to activate the drawbar.

I would prefer to "electrically" disable the drawbar when the spindle is active and eliminate the microswitch mechanism. I saw a few older posts on this topic that I did not fully understand and required macros to accomplish the task. Being very new at this, I would prefer not to use a "programmed" approach as sometimes there are situations that are not anticipated that the program does not account for. There is also a timing element where there can be no power to spindle, but the spindle could still be coasting.

Is there a simple way to accomplish this? Is there an output that is open or closed when the spindle is active?

I am using a DuraPulse GS20 VFD and believe that there is a pair of dry contacts that can be opened/closed based upon the spindle status. The VFD even "knows" the braking time etc. I think the problem with using the VFD is that it may be able to verify that the spindle is stopped allowing you to activate the drawbar, but it may not stop you from turning on the spindle while the draw bar is active. Perhaps an additional relay or set of contacts would be needed to accomplish this. Is this a safe approach or are there some issues I need to be aware of?

Please let me know your thoughts.... Richard

[Ken Rychlik]

Most VFD's have a (spindle stopped) output available. You can use this with a mechanical relay to not let the drawbar operate when the spindle is moving. You could also send that as an input to acorn and in the programming there are options to (wait for spindle stopped) before going forward with the task. On a router, I use (tool holder open) and (spindle stopped) to build in some safety. If the drawbar does not open as expected, the program stops the atc file from proceeding. On mine forgetting to turn on the air supply is the most common human mistake.

I like the approach of doing both mechanical and software.

[tblough]

There should already be a spindle enable command from the Acorn. You should be able to use a relay to energize your drawbar only spindle enable was off.

[Muzzer]

I use the "spindle stopped" signal in conjunction with the spindle top switch to enable the drawbar. That way it can only operate when the spindle is fully retracted and is stationary.

[suntravel]

You can use the input VFDZeroSpeed to make sure the spindle is not running, or use the variable #25009 in a macro.
#25009 is the spindle speed, so you can check that it is = 0 before activating the draw bar.

Uwe

[cncsnw]

Note that CNC variable #25009 is only available if you have a spindle encoder installed, and have set Parameter 78 to report spindle speed based on the encoder.

Assigning inputs for ToolUnclampButton and VFDZeroSpeed, and an output for UnclampTool, should make it work as it should. Of course, you have to configure your VFD to provide a reliable zero-speed signal to the VFDZeroSpeed input.

[RJS100]

Thanks for all the nice ideas. Very much appreciated! It just so happens that on my mill, the VFD, power drawbar switch & drawbar solenoid happen to be physically adjacent to each other. Therefore, a VFD driven solution would undoubtedly be the easiest to implement.

The switch that currently activates the drawbar contains both N/O and N/C contacts. See crude sketch below as I plan to use the dry contacts on the VFD to break that circuit that activates the drawbar when the spindle is active. Simultaneously I will use the N/C contacts of the drawbar switch to break the "VFD" common circuit which will disable the spindle when the drawbar active.

There is one event that this safeguard does not appear to work completely. If the spindle is stopped, and the drawbar is active AND you press the "Auto-Spindle-Manual" to operate the spindle manually, then press "spindle on", nothing will happen at that moment. However, when drawbar is released, the spindle can start spinning before the drawbar is fully retracted. Is there some way to prevent this without the use of another set of contacts that are active when the drawbar is fully retracted? I think there may be a VFD parameter that will add a time delay each time the spindle is activated.

Is there some other event that I am not aware of where the drawbar could be activated when it should not be able to?

Best... Richard

[RJS100]

OK... I wired up as shown below, and noticed that there is a problem. The drawbar only operates when the spindle is stationary. Great! However, if the drawbar is activated AND the spindle is turned on manually (Manual Override).... as soon as the drawbar is released, the spindle will begin to turn. You could still be holding the tool at this moment. Not Good!

Is there a way to use an input like "DrawBar Clamped" or "SafetyDoorLockConfirmed" to tell CNC12 that the drawbar is active and therefore ignore any manual attempt to start the spindle?

Thanks... Richard