anilam feedback

[ironDigit]

i've just picked up some "real nice servo's"
they came from a cnc bridgeport using anilamcontrol wich had lost its DRO's

wel here's my question and i hope some1 can shed a light on this one cause it looks like i got sc***** real bad.

i assumed that all servo motors have a feedback built into the motor itself. But the more i read about the anilam controls the more i'm geting the idea that the only feedback anilam uses are the dro's and not the encoder like i'm used encountering here on the zone.

this meaning that the motors i got are "plain" steppers with no feedback possibillitites whatsoever.

SEM Small Electric Motors London permanent magnet DC servomotors is what the lables on the motors say 75v at 22amps 1,1NM 2500 and i also got some 400RPM models.

what i eventually would want to know is if i can run these babies with "regular"servo controllers like the UHU and still have feedback on what the motors are actually doing ?or will i have to install some encoders meself ?

did i get burned or can you indeed call these motors servo's without the feedback without lying ofcourse ,cause if there's no feedback now i'm feeling kinda ....

[One of Many]

SEM motors are servos. If they say servomotor, they would not be steppers, but could be used as steppers via a servo amp controlled in that manner. I do not know how Anilam used feedback. They could have a cap/cover on the end of the motor that covers a rotary encoder or they could have used linear scales on each axis. You will need one form or another for feedback if you plan on a closed loop system. Consider it an opportunity to select your own resolution based on the rest of the system, such as lead screw pitch, pulleys etc. Encoders are not that hard to find used, which is rather risky in and of itself.

DC

[RogerN]

I have to Anilam machines, a Bridgeport with a Crusader II control and a lathe with a Crusader M Lathemate control. Both use SEM servos with tachometer feedback to the servo amp and encoder feedback to the control itself. The mill uses DRO scales for position feedback and the lathe uses encoders on the ball screws.

I never got the control to work on the lathe so I replaced it with a PC running EMC2 and a $199 Mesa 5i20 board and a $69 analog interface board (My drives take a +10V to -10V analog signal).

There a 2 choices I can think of right off. 1. You can get some servo amps with tachometer feedback and use either rotary or linear encoders for position feedback. 2. You can get some encoders and not use the tach feedback, just use a drive with encoder feedback. If you add the encoders, you could use something like Gecko drives and use software that uses step and direction output.

What I like about the mill is that by positioning off DRO scales, I am positioning the table to the desired position, not just the motor. I can have lead screw error and backlash, but my position is always gets right on to the DRO scale position. While it is more expensive to close the loop for velocity with the tachometer, then again for position with the encoder and controller, it gives more accuracy for a less than perfect system.

Hope this helps
RogerN

[ironDigit]

thx guys ,

The profit of using both lineair as servo-encoders sure makes for solid positioning accuracy but with ground ballscrews i'm not worrying about positioning accuracy but more about the motors doing what they are told /asked and getting some feedback from them.

wich brings me to the matter of me not being able to establish weather these SEM motors got some means of feedback built-in and i should just drive them with the UHU drives or will i need the complete control including lineair encoders if i actually think i need te feedback function.

they do seem to have some cap over the end like ONE OF MANY mentioned and on the wiring scheme's there is a tacho mentioned in the motors>controller wiring.

thats also the reason that kept me from just unscrewing the end(cap) cause if there is a encoder installed i'ld be damn disappointed if i drop it out a there meself and i got no skills when it comes to motor electronics.9i hope i'm just overestamating things but rather sure then sorry)

would any motor lacking feedback be worthy of being called a servo instead of a stepper anyway /?


THX for reading !

[One of Many]

Pragmatically speaking, DC servo motors are typically a permanent magnet field and a brushed armature. Without feedback they are just a DC motor. There are some servo amps that will make a DC servo act like a stepper motor, but they too require feedback.

Stepper motors have a permanent magnet armature and several field coils energized via the stepper driver electronics. These are controlled by step and direction signals not necessarily requiring feedback since the position is presumed relative to steps in memory. The risk lies in lost steps since the control is not a closed loop tracking true position. Some systems do offer that option though.

Ground ball screws do not mean there will be no pitch lead compensation required. If the original machine had a rotary encoder, either they used zero backlash precision lead screws or there is a Ball screw compensation table in the control parameters to correct for pitch lead along the screw electronically. With linear encoders, there would be less need for compensation to the screw, but there may be some for the linear scale itself. A linear encoder can be precise inch for inch, but can ebb slight errors over longer distances. Most likely less than the precision of the machine tool itself, so it is usually not that much of a concern under 30" of travel for each axis.

Some SEM motors do have both Tach and Encoder inside the cap. Removing the cap should be fine. If there is an encoder in there, there will also be a mount for the encoder that can be removed to see if there is a tach portion internally. The wires coming out of the motor should give some indication of that too.

The question I would have relative to what I have read here in the Zone is finding compatible servo amps to drive some SEM motors. Those SEM servos in question on other OEM applications may have had odd voltage and current requirements that forced the retrofit to new motors and amps that are known compatible. If you have the original servo amps, you may be in luck.

DC

[Al_The_Man]

The SEM are nice motors and sought after because they were fitted to quite a few machines in their day.
As mentioned They usually are fitted with tach and encoder, todays drives are generally operated in the torque mode rather than velocity, so it make the tach redundant and can be disconnected/ignored if retro fitting.
For analogue type drivers there are several A-M-C drives that will operate these motors.
Also if you use them for a spindle motor, (they are usually 4000rpm), they can be run off of the common SCR type DC drives available, if you obtain 4 quadrant for regenerative braking and use the tach for precise speed, you get almost servo control from the spindle.
Al.

[RogerN]

If your motors are like mine, they only have tachometer feedback. As they are, with the right amp, their feedback is good for velocity, not position. If your ballscrews are the precision you want, you could do like what it done on my lathe. The encoders are coupled directly to the ball screws, there is a tooth belt between the motor and the ballscrew.

I use the amps that came with my lathe but replaced all the amps in the mill with AMC (a-m-c.com) amps. They wanted over $800 each for new OE amps, the AMC amps were $335 each. AMC Amps often show up on eBay for quite a bit less than new price. I had to replace the spindle encoder on my lathe and used a "medium duty" one for ~$130 from Automationdirect.com.

If this seems like more than you want to deal with, I have seen some Anilam CNC stuff bring pretty good money on eBay. I assume people buying parts for replacement or spares that are hard to find these days.

Good luck
RogerN