A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. It divides a full rotation into a number of equal steps. A stepping motor is driven by a series of electrical pulses, which are generated by the MCU in an NC system. Each pulse causes the motor to rotate a fraction of one revolution, called the step angle. The possible step angles must be consistent with the following relationship: ∝=360ns
Where α = step angle (degrees), and ns, = the number of step angles for the motor, which must be an integer. The angle through which the motor shaft rotates is given by Am=np∝
Where Am = angle of motor shaft rotation (degrees), np = number of pulses received by the motor. Advantages
1. The rotation angle of the motor is proportional to the input pulse. 2. The motor has full torque at standstill (if the windings are energized) 3. Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3 – 5% of a step and this error is non-cumulative from one step to the next. 4. Excellent response to starting/stopping/reversing.
5. Very reliable since there are no contact brushes in the motor. Therefore the life of the motor is simply dependent on the life of the bearing. 6. The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control. 7. It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft. 8. A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses. Disadvantages
1. Resonances can occur if not properly controlled.
2. Not easy to operate at extremely high speeds.
DC brush motors rotate continuously when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets arranged...
References: Reston Condit and Douglas W. Jones (2004). Stepping Motors Fundamentals. Microchip Inc.
Mikell P. Groover (2007). Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition. Prentice Hall, ISBN 0132393212
Bela G. Liptak (2010). Instrument Engineers ' Handbook, Fourth Edition, Volume Two: Process Control and Optimizatio. Taylor & Francis, ISBN 1420064002
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