ToolsUnclamped Sensor - Power Drawbar

[RJS100]

One of the inputs for the Automatic Tool Changer is a "ToolsUnclamped" sensor. I have a power drawbar that uses a pneumatic ram that compresses a set of Belville washers and unclamps the drawbar when the ram is extended. The stroke of the ram is roughly .3 inches. I am not sure what kind of sensor to use to sense the "ToolsUnclamped" position. Any idea of what is typically used?

Here is a very quick video: https://www.dropbox.com/scl/fi/1kevnqyr ... 8tekd&dl=0

Richard

[cncsnw]

Most common is a pair of normally-open electro-mechanical micro switches, detecting some piece (often an add-on metal tab cantilevered out from the drawbar assembly) as it moves up and down.

There is a good picture of the switch assembly that Atrump uses on their machines, here:
https://www.atrump.com/images/tech_supp ... switch.pdf

The switches are mounted in slots, so you can adjust them up and down until they just trip when the tool is fully clamped, or fully unclamped.

[RJS100]

Thanks Marc. That is very helpful. Just curious if you think a proximity sensor could work also? Looking at the way the power drawbar was built, it may be easier to mount proximity sensors.

I noted that your illustration shows a micro switch for clamped AND unclamped. The Centroid schematic only shows a ToolsUnclamped input (see attached). Are you suggesting that I use both?

[cncsnw]

You will have to judge that for yourself.

ATC PLC programs for non-Acorn controls, where there is sufficient I/O, nearly always use separate switches to confirm both unclamped (so they know when it is safe to move the head up after unloading a tool, without ripping the fingers out of the carousel) and also clamped (so they know when it is safe to retract the carousel without dropping the tool on the table, and also know it is safe to start the spindle turning).

I would not be surprised if the Acorn programming omits the tool-clamped switch, as a concession to the limited I/O in the Acorn system.

[RJS100]

Thanks Marc. Since I purchased the Ether1616, I now have sufficient inputs/outputs and would be happy to use them wherever necessary.

I looked closely at the documentation and found the following:

1. With Acorn, there is no "ToolClamped" input. It does exist with Hickory, but not Acorn. Therefore, I would guess that the standard PLC programming for the ATC does not address the ToolClamped status.

There is a DrawBarReleased input, but I understand that this serves as an indicator and displays the DrawBarReleased status.

In attempt to use inputs/outputs for best possible ATC function, I see there is also:
ATC_AirPressureOk - Input
AirBlowNozzle - Output

Do you know if the standard PLC programming for the ATC addresses these? I believe in a previous post, you mentioned that you can also use UnclampTool to activate the nozzle to blow debris off the tool. I wonder how this would differ from the AirBlowNozzle.

Thanks... Richard

[suntravel]

You will need to edit the PLC to stop all action with an input detecting ToolIsClamped.

If you use ChuckIsClamped for this purpose default PLC action is to prohibit SpindleStart, but not ripping out an unclamped tool from the ATC.

ATC_AirPressureOk if not set will also prohibit to unclamp the tool.

Both will output a senseless error MSG.

So, IMHO the best way is to use a free input, edit the PLC, ATC macro and plcmsg.txt

I the drawbar is going up further if it is clamped and no tool in the spindle I would mount the ToolIsClamped sensor that it is not set if there is no tool in the spindle to generate a No tool in the spindle fault.

Uwe

[RJS100]

I find this a bit confusing. My first question at the start of this tool changer project was to clarify if custom PLC type programming was required for the ATC to operate properly. I understood that the Wizard would create the PLC programming to support the referenced schematic. I wanted to avoid PLC programming at this time.

Marc's explanation "(so they know when it is safe to move the head up after unloading a tool, without ripping the fingers out of the carousel) and also clamped (so they know when it is safe to retract the carousel without dropping the tool on the table, and also know it is safe to start the spindle turning). all appear to be very important.

I have no experience here... so it is hard for me to know if these safeguards are unnecessary, and that is why Centroid omitted them. With plenty of extra inputs/outputs, I would rather have them.

Uwe, I am afraid I do not understand your note: If the drawbar is going up further if it is clamped and no tool in the spindle, I would mount the ToolIsClamped sensor that it is not set if there is no tool in the spindle to generate a No tool in the spindle fault. From what I can see, there is no ToolsClamped sensor with Acorn.

Here is a video that shows this exact same tool changer being controlled with a Masso controller. At 4:30, you can see the biggest challenge.




Since TTS tool holders need perfect alignment, it seems to me like having these extra safeguards would be particularly important during initial setup. I wish I knew this at the beginning.

How involved is the PLC programming to add this safeguard? Is it costly?

Richard

[suntravel]

You can use the ATC without PLC work as it is, if you want more safety features the DIY part of configuring the CNC comes in.

A draw bar like an automatic chuck will have three possible positions you can request with sensors/switches

Tool unclamped
Tool clamped
Clamped without a tool

OTB Acorn is prepared only for Tool unclamped. That is ok but not the maximum safety possible.

Uwe

[cncsnw]

Regrettably, I do not have time to read through the current Acorn PLC program and documentation to tell you what inputs are used, for what purposes.

To expand on what Uwe just said:

The information you can get from tool-unclamped and tool-clamped sensors varies with drawbar design.

Tool-clamped sensors, one way or another, almost always tell you that the jaws are fully open and the tool is free.

A tool-clamped sensor like the one on Atrump machines (and many larger machining centers) only tells you that the release cylinder is fully retracted, and is no longer touching the top of the spindle or compressing the Belleville washers. It cannot tell you whether the tool holder is present, or whether the tool holder is properly clamped.

Many integrated ATC spindles incorporate the sensors and the release cylinder into the top of the spindle. Because the drawbar can retract higher up when there is no tool holder in place, it is possible to make the tool-clamped sensor close only when the drawbar is in the clamped position, and a tool-holder is present; or to provide three sensors instead of two, so that the "cylinder up" and "tool present" conditions can be detected independently.

Because tool-clamped switches and conditions can vary, and are not always present at all (see Fadal), I can see why Centroid may have decided to omit them altogether when they set out to write a universal, one-size-fits-all PLC program for the Acorn.

You have said you are working on this project to develop/refine an "Acorn compatible" ATC. In the area of tool-clamped sensors, you probably have to decide whether it is just "Acorn compatible", or whether it is going to target a specific type of machine tool, spindle, and drawbar.

If you want it to be as broadly applicable as possible, without requiring machine-specific revision for each installation, then you should probably omit the tool-clamped sensor.

[RJS100]

Marc, thanks for your thoughts. As this is completely new to me, I appreciate your insights.

You are correct in that my goal is to refine an Acorn compatible ATC. At this point, I will pull a few extra lines for possible additional inputs/outputs in the future and wire per the schematic at this time.

Best... Richard