Step Motors Question

[titolex]

I need to buy a new drive for an step motor, but I have a big question...The motor is a 200 step/rev and the drives that I have found have a bigger resolution, like 1000 step/rev...So, If I buy a drive with a highter resolution, my motor will work??

Thanks for your time
eng Jose Gregorio
22/11/2005

 

[MikeHalloran]

I'm guessing the drive spec you're quoting is for a microstepping mode. Read the drive docs to see if it can 'full step'. That would be 200 step/rev for a common step motor.



Mike Halloran
Pembroke Pines, FL, USA

 

[fsmyth]

Since the advent of cheap(er) silicon, it seems that almost
all the vendors are tending toward adding micro-stepping to
their drives. There is almost always (at least on decent
drives) a way to control steps/rev. Specs will tell you.
The 200 steps/rev is a function of the motor's physical
construction. Micro-stepping (simply) allows drive to
rotor angles not at pole positions. In fact, you may find
it beneficial in your application.
Bottom line, any drive with a higher resolution than your
motor should work. Stick with a reputable manufacturer,
especially on the larger drives.
<als>

 

[Barry1961]

I am guessing that you have already matched the number of phases, voltage and wether it is unipolar or bipolar windings.

Barry1961

 

[cswilson]

I wouldn't worry about the drive being incompatible with the motor in this way (although there are other ways in which the drive could be incompatible with the motor -- voltage, current, phases, etc.). The drive has no way of "knowing" how many steps per revolution the motor has, nor does it "care".

It is important to understand the concepts behind the terminology. A "200-step" 2-phase motor is a 100-pole motor -- it has 50 north/south pole-pairs per revolution. In the simplest way of driving it, called "full stepping", there are 4 "steps" per pole-pair (A+B0, A0B+, A-B0, A0B-). Traditional stepper drives would transition from one of these states to the next every time they received a pulse input from an indexer.

As fsmyth pointed out, it is now often economical to create more setpoints within a pole-pair of the motor. Instead of just switching current on/off in phases, they apportion current in the phases. Think of Phase A becoming "sine" and Phase B becoming "cosine", with the resulting angle within the pole-pair's electrical cycle (1 electrical cycle = 7.2 mechanical degrees) being the arctangent of these values.

If your drive is advertised as a "1000-step" drive, it probably means that it generates 5 "mini-steps" per full step of a motor (20 per electrical cycle), so that on the most common type of stepper motor (the type you have), it can resolve a mechanical revolution into 1000 parts (0.36 mech deg). For each pulse that it receives, it advances its phasing by 18 electrical degrees (1/20 elec cycle). You should look a little more deeply into the drive literature to see that this is indeed the case.

So I think you are looking at what is commonly called a "mini-stepping" drive. Drives that create hundreds or thousands of increments per electrical cycle are commonly calle "micro-stepping" drives.

I see no reason why you could not use this drive for the motor if it is otherwise compatible, but you will need to generate 5 pulses for every 1 that you would generate in full stepping mode.

Curt Wilson

 

[cswilson]

Hmmm...I generated a smiley without intending to. The sunglass smiley should just be "B-)". Gotta remember to preview...

Curt Wilson