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Stepper Fundamentals Slide 45

The designer must select operating points that are below the speed-torque curve or the motor will loose steps and stall. A typical way of operating a motor would be to select a value at around 75% of the torque curve and then be sure to operate on or below that point, and do not operate on any of the mechanical resonance points. Obviously the designer must consider the desired operating speed and the available torque. In the diagram, the vertical green line may represent the desired operating speed. This may be dictated by a requirement to match a speed or to make a movement within a certain amount of time. The available torque for a design point at that speed is shown on the vertical axis. However, the torque required to start the motor moving may be much higher than that. The horizontal blue line represents the amount of torque needed to overcome the inertia and friction of the system to get the load moving. At this point the maximum speed is much less than the desired speed. Fortunately as the speed increases, the load due to the inertia decreases and, in most cases, less torque is needed to keep the load moving than to accelerate or decelerate it. So as the motor gets moving, less torque is typically needed and acceleration can happen a bit faster. The simple solution is to create an acceleration and deceleration profile to start and stop the motor.

PTM Published on: 2011-12-14