DickDV
Member
ArikBY, sorry about the lecture. I didn't mean it for anything other than useful information among us techies.
I can only speculate about the manufacturers' reasons for the oversize and I would guess that there is a comfort level that comes from overdoing a design especially when the technology is new. These manufacturers have their reputation to protect just like we do and most are being very conservative. I predict that, as they get used to the technology, they will begin reducing their systems back down to the real load demands. Also, engineers seem to be very reluctant to embrace AC motor overspeed operation. The manufacturers publish overspeed info in their motor manuals but that doesn't seem to convince many of them.
On the other hand, I trust the numbers and am willing to take moderately more risk. This is possible for me because I have been associated with ABB for over ten years and have become very comfortable with their published specs. I have pushed their drives to the end of reasonable limits and have not been dissappointed especially with their DTC drives, ACS600 and now ACS800.
Using DTC, you can expect full motor torque at zero speed in speed regulation mode. I have done it and have seen it demonstrated with hanging loads on a hoist. Torque control mode does not require an encoder and, again, full rated torque is available at zero speed.
For those extruders, A DTC controlled drive can resolve out about 90% of motor slip from no load to full load. Extruder loads typically don't change much so speed regulation is rarely an issue.
As for rotor/load intertia matching, I am not a servo tech and wouldn't claim to be. However, as I understand it, interia matching is primarily a tool to improve dynamic response as in step-change torque inputs, etc. AC drives and most commodity grade DC drives are not intended for such applications and, I assume, for that reason, I don't run into those kinds of issues.
I can only speculate about the manufacturers' reasons for the oversize and I would guess that there is a comfort level that comes from overdoing a design especially when the technology is new. These manufacturers have their reputation to protect just like we do and most are being very conservative. I predict that, as they get used to the technology, they will begin reducing their systems back down to the real load demands. Also, engineers seem to be very reluctant to embrace AC motor overspeed operation. The manufacturers publish overspeed info in their motor manuals but that doesn't seem to convince many of them.
On the other hand, I trust the numbers and am willing to take moderately more risk. This is possible for me because I have been associated with ABB for over ten years and have become very comfortable with their published specs. I have pushed their drives to the end of reasonable limits and have not been dissappointed especially with their DTC drives, ACS600 and now ACS800.
Using DTC, you can expect full motor torque at zero speed in speed regulation mode. I have done it and have seen it demonstrated with hanging loads on a hoist. Torque control mode does not require an encoder and, again, full rated torque is available at zero speed.
For those extruders, A DTC controlled drive can resolve out about 90% of motor slip from no load to full load. Extruder loads typically don't change much so speed regulation is rarely an issue.
As for rotor/load intertia matching, I am not a servo tech and wouldn't claim to be. However, as I understand it, interia matching is primarily a tool to improve dynamic response as in step-change torque inputs, etc. AC drives and most commodity grade DC drives are not intended for such applications and, I assume, for that reason, I don't run into those kinds of issues.