Automatic Tool Changer (ATC) Dropping Tools? 5 Things to Check
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A very common source of machine malfunctions is the machine’s ATC (automatic tool changers). I think this is due to the mechanical complexity of the ATC. There are many fast moving parts and every part and adjustment has to be basically perfect in order to execute a proper tool change.
Today I want to discuss a particular problem with tool-changers. This is the problem where the ATC is dropping tools during the ATC cycle. There are of course more possibilities for this phenomenon than I will mention, but I would consider the 5 check points listed below as the “usual suspects”.
It is always preferred to run the ATC manually (with a hand-crank possibly) or slowly using the motor (in an ATC adjutment mode), in order to observe exactly what problem may be happening. The correct method will depend on the machine. On a modern CNC machine with a quick tool-changer, it’s probably the only way you’ll be able to tell what’s going on.
1. ATC GRIPPER ALIGNMENT TO THE TOOL HOLDER IN THE SPINDLE: TOOLS DROP ON THE SPINDLE SIDE
After a crash, the alignment of the gripper to the spindle tool may be off. In many cases, the arm is held to the main shaft by use of a compression coupling. This may also be referred to as a “Mech-Lock”. Although this is a very secure fastening method (since it squeezes the main arm shaft as well as expanding inside the bore of the arm), it will still slip if there is a significant impact (like a tool hitting a fixture during the ATC cycle, or maybe the ATC trying to load a tool on top of another tool that wasn’t supposed to be there (usually a self-induced tool data problem).
It may be that a misalignment is being caused by an incorrect axis position. This may occur if there were a crash that changed the axis position for the ATC cycle (usually G28 or G30 position). If an axis ballscrew has slipped in it’s relationship to the motor and the motor encoder is what’s tracking the axis position (as opposed to a scale, for example) the machine does not know that the ATC point (and every other position for that axis) is incorrect. It will probably still attempt the ATC function and the holder will probably hit something.
A small amount of position error (as little as 25micron in some cases) can result in a change in the ATC function. An ATC alignment tool, like the one pictured below, is essential in determining the correct ATC position:
2. ATC GRIPPER ALIGNMENT TO THE TOOL HOLDER IN THE WAITING POT: TOOLS DROP FROM THE WAITING POT (MAGAZINE) SIDE
If you are dropping tools on the waiting pot side of the arm, you may have an alignment issue of the arm to the wiating pot. Check to see if there is a problem with the position of the waiting pot. If the pot swings from the magazine to the waiting position (M06 position), there may be a stopper that is misadjusted or broken. In many cases, the tool-holders are held in the waiting pot by spring-loaded balls that snap in around the pull-stud of the holder when the holder is inserted into the pot by the ATC arm.. These balls may not be moving freely or may be missing. This condition may have the tool-holder held loosly in the waiting pot when the ATC arm swings in to grab it. This may cause alignment issues with the gripper, resulting in tools dropping. This may also allow the tool-holder to drop out when the ATC arm moves away from the pot, toward it’s home position, at the end of the ATC cycle.
3. TOOL-HOLDERS ARE LOOSE IN THE MAIN ARM: TOOLS HOLDERS DROP DURING ARM TURN MOTION
Is the tool-holder being held tightly in the gripper during the rotation part fo the arm motion? If it’s not, it’s very posssible that the rotation may launch the holder while the arm is turning. If it is possibleto stop the ATC in the middle of it’s cycle (the rotational part), you may find that the tools are loose in the gripper. I’ve found in many cases that this is the result of a faulty tool-lock function. The arm will have some type of tool-lock device to hold the tools in the gripper during the turning motion. Older machines sometimes had actual hydraulic locking cylinders built into the arm for this purpose. Newer machines will likely have some mechanical device for the job. Something is suppposed to hold the tool-holders tightly when the arm spins. If you can pull the tool out by hand during the portion of the ATC cycle when the arm is turning, something is probaly wrong with the tool-lock.
It maybe the case that the gripper is damaged from impact or wear, and no longer conforms to the shape of the tool-holder flange. This would probably be on one side of the arm more than another, if this were the case, since the two sides would prbably not both be damaged or worn identically. Again, you shouldn’t be able to just pull the holders out of the arm during the turn. Obviously, I mean when the arm is stopped at a point where it would normally be turning. Don’t touch the tools or the arm while the arm is turning, in case your a person who hasn’t figured that out already. Had to say that, just in case. If you can pull the holder out, maybe the gripper(s) are bent or worn out.
4. IS THE DRAW-BAR, COLLET OR RETENTION KNOB (PULL-STUD) THE PROBLEM?
Broken collet fingers, draw-bar moving too slowly, draw-bar stuck? What about the pull-stud? Is it correct for the machine? Is the draw-bar timing wrong? I know several machines where the hydraulic functions of the draw-bar are controlled by the position of the servo motor turning the ATC. If the relationship between the motor and the ATC changes, you may have problems holding on to the tools.
5. IS THE TOOL-HOLDER WITHIN MACHINE SPECIFICATIONS IN TERMS OF SIZE AND WEIGHT?
Honestly, I can’t remember many times that a machine started dropping tools due to a specification problem. I’m not saying that it doesn’t happen, it’s just that I haven’t seen it alot. Now, I’ve seen alot of people run tools right at the limit. But, the limit is the limit and if you’re under you’re under. It should work. In most cases, it has worked for a long time, but doesn’t work anymore. Something has changed. I do remember finding underlying problems that ultimately solved the tool dropping when corrected.
One instance that is related would be a machine that has a “heavy-tool” function that uses a slower ATC speed that is not being specified in the program. For example, on alot of Toyoda machines, M16 is the heavy-tool m-code. If you decide to change a heavy-tool with M6, the machine will try to do it. However, you had better have the door closed when you do it because that tool may fly out of the arm.
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Tagged With atc, atc gripper, automatic tool changer, gripper, pull stud, retention knob, tool holder, tools