EDM again
Posted by
Marcus & Eva
on 2001-08-06 20:56:24 UTC
Hi all:
I am starting on the design for my orbiting head (for a sinker EDM) and
I have some design issues that I don't have the expertise to sort out.
I am hoping that some of you can get me pointed in the right direction.
For those of you that are unfamiliar with what an orbiter does, it is a
device that mounts to the ram of a manual sinker EDM to allow the electrode
to move in the X and Y directions while the Z axis drives the electrode into
the workpiece.
This additional motion has some big benefits in the EDM process.
The necessary operating criteria, as far as I can tell are as follows:
1) it needs to move in X and Y only a small amount; 0.015" in either
direction per axis is plenty for most applications.
2) It needs to be very precise in its motion; of the order of 0.0001" to
0.0002" positioning error compared to where the control tells it to be. It
has to be able to move a 50 lb slide system and electrode total weight
around at maybe 10" per minute. Faster acceleration is better, but faster
top speed is of no value.
3) The system needs to be able to move in a preprogrammed "canned " motion
cycle but it needs also to be responsive to the spark gap voltage in exactly
the same way that the Z axis ram is responsive to spark gap voltage. The
canned movement patterns are extremely simple(all linear moves; either one
axis at a time, or both axes together).
A decrease in voltage below a preset value has to trigger a stop of the
advancing axis or axes (if two are moving simultaneously) and a further
decrease has to trigger a backup move of that axis or axes, followed by a
return to the previous positions when the voltage rises above a preset
value, followed then by continuation of the canned cycle.
My questions are as follows:
1) Can any of you come up with a better way to move the axes than ballscrews
and ballnuts?
It seems a shame to couple a pair of servos or steppers to ballscrews for a
total travel of 0.030" per axis.
Could it be done with a linear motor or with an eccentric (like a crankshaft
and connecting rod)
2) How do I get the precanned cycle to be responsive to spark gap voltage?
I know that I could make the basic moves with G code, but again, it seems
overly elaborate to me when all I really want to do is set up one of maybe
twenty patterns of signals to the motors and make the choice of whether to
proceed or retreat based on the voltage sensed across the spark gap.
3) Can I realistically utilize the existing control ( which obviously has to
send a spark gap voltage dependent signal to the Z axis servovalve) to set
conditions in which either motion A(advance) or motion B (retreat) is
performed by the two motors of the X and Y axes? Simultaneously??
Simultaneously with the Z axis too???
4) Have I missed anything obvious and important in my description of what
has to happen?
I will be most happy to hear any ideas that any of you may have.
Thanks in advance
Marcus
I am starting on the design for my orbiting head (for a sinker EDM) and
I have some design issues that I don't have the expertise to sort out.
I am hoping that some of you can get me pointed in the right direction.
For those of you that are unfamiliar with what an orbiter does, it is a
device that mounts to the ram of a manual sinker EDM to allow the electrode
to move in the X and Y directions while the Z axis drives the electrode into
the workpiece.
This additional motion has some big benefits in the EDM process.
The necessary operating criteria, as far as I can tell are as follows:
1) it needs to move in X and Y only a small amount; 0.015" in either
direction per axis is plenty for most applications.
2) It needs to be very precise in its motion; of the order of 0.0001" to
0.0002" positioning error compared to where the control tells it to be. It
has to be able to move a 50 lb slide system and electrode total weight
around at maybe 10" per minute. Faster acceleration is better, but faster
top speed is of no value.
3) The system needs to be able to move in a preprogrammed "canned " motion
cycle but it needs also to be responsive to the spark gap voltage in exactly
the same way that the Z axis ram is responsive to spark gap voltage. The
canned movement patterns are extremely simple(all linear moves; either one
axis at a time, or both axes together).
A decrease in voltage below a preset value has to trigger a stop of the
advancing axis or axes (if two are moving simultaneously) and a further
decrease has to trigger a backup move of that axis or axes, followed by a
return to the previous positions when the voltage rises above a preset
value, followed then by continuation of the canned cycle.
My questions are as follows:
1) Can any of you come up with a better way to move the axes than ballscrews
and ballnuts?
It seems a shame to couple a pair of servos or steppers to ballscrews for a
total travel of 0.030" per axis.
Could it be done with a linear motor or with an eccentric (like a crankshaft
and connecting rod)
2) How do I get the precanned cycle to be responsive to spark gap voltage?
I know that I could make the basic moves with G code, but again, it seems
overly elaborate to me when all I really want to do is set up one of maybe
twenty patterns of signals to the motors and make the choice of whether to
proceed or retreat based on the voltage sensed across the spark gap.
3) Can I realistically utilize the existing control ( which obviously has to
send a spark gap voltage dependent signal to the Z axis servovalve) to set
conditions in which either motion A(advance) or motion B (retreat) is
performed by the two motors of the X and Y axes? Simultaneously??
Simultaneously with the Z axis too???
4) Have I missed anything obvious and important in my description of what
has to happen?
I will be most happy to hear any ideas that any of you may have.
Thanks in advance
Marcus