Stepper Motor misses steps prior to reaching its physical limitations during sinusoidal motion

[nstroud]

Hello,

  My end goal is to move a x-y stage (via 2 linear actuators) in a circular motion (radius of 0.47") at a rate of 1Hz. I am running the example VI "Circle Demo" that was provided with my copy of LabView, version 9.0.

  The problem that I am encountering is that given the physical limits of the motor and motor drive, the task should technically be attainable (see calculation*). However, even when the motors are completely unloaded (not attached to anything), they begin missing steps far short of my end goal. I am only able to achieve a radius of 0.2" (peak velocity of 1.25"/second).

My question; Is the system configured incorrectly, or is my end goal unrealistic given unavoidable performance reductions due to software/hardware?

  I apologize for the naiveté of this question, but if there is any information that you could provide that would shed some light on this problem, I would greatly appreciate it.

Potential Theories:

Torque is further diminished at higher speeds due to microstepping

A closed loop system would improve performance at higher speeds

The VI "Circle Demo" is not the best method for creating a circle

The peak acceleration is the limiting factor, not velocity

*Radius = 0.47"

Peak Velocity = (Radius * 2 * pi) * cos(2 * pi)

Peak Velocity = 2.9"/second

System:

LabView v9.0

PCI-7340

open-loop configuration

MID-7604

1.4A per axis

10 micro steps

Linear Actuator (data sheet is attached)

NEMA-17 stepper motor (Sold by ultra-motion).

3.3 inches/second maximum velocity

1.2A coil-current

1.8º step angle

Regards,

Nick

[Brian_Beal · Accepted solution]

Nick-

I really question the max velocity in the spec sheet.  0.0833"/rev at 3.3"/sec=about 40RPS (2400RPM), which is extremely fast for a stepper motor, especially at 24VDC.  Find out exactly which motor is on the actuator, and go to www.applied-motion.com and you should be able to find torque curves for that or a similar motor with various drives.  You will see that the torque curves at 24VDC are not good.  Also, ask Ultramotion if their speed/force curve is theoretical, or if actual tests were done.

[Brian_Beal]

Nick-

Have you found out anything else about this?

[nstroud]

Brian,

  Thank you for your reply, it has helped narrow down the issue. I believe the main source of error is that the motors are underpowered. The motor specifications may be a little overestimated (the manufactureres suggested I increase the voltage to 48V), but only providing 1A RMS at 24V instead of 1.7A at 24V appear to be the main issue.

  Changing the wiring of the motors from serial to parallel has helped (now reaching approximately 2"/second), but I have yet to observe their performance under load.

Thank you again,

Nick