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17 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are 4 types of motors? |
DC motors AC motors Stepper motors Linear Motors |
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What is a stepper motor? How is it controlled? What are some advantages? |
Type of DC motor which moves in accurate measurements. Controlled by digital pulses. Easy to implement hardware and software. Accurate positioning |
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What are two types of stepper dc motors? |
Variable reluctance stepper Permanent magnet stepper |
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Describe variable reluctance stepper? How does it work and what is reluctance? |
Has a ferro-magnetic (soft iron) rotating shaft. Opposite pair of windings are energized to produce magnetic field. Magnetic flux will pass from stator piled to nearest rotor set which will be the shortest path and path of least reluctance |
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What is permanent magnet stepper motor? |
Has rotor of permanent magnetics and stator of electromagnetics. Rotor is controlled by switching polarities of stator coils. Has detent torque. |
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What is detent torque? How does it occur? |
The permanent magnetic stepper motor can remain in position and withstand opposing torque, even when coils are not energized. This is because of the attraction between electromagnetics and magnets, so induced current produced which needs torque to overcome. |
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Stepper motor terms Phase? Step angle? Poles? Holding torque? |
Phase = number of independent windings Step angle = angle rotor moves for one switching change of stator coils. Poles = magnetic polarity terminals. Holding torque = the torque needed to move the motor once energized. Detent torque is not energized. |
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What is locked step mode? What is slewing mode? |
Locked step Motor decelerates or might stop between steps. Motor can be started or stopped instantaneously without losing position. Slewing mode Too fast to allow instantaneous start/stop. Must be slowly put in and out of mode. It does not settle between steps |
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What is a uni or bipolar motor? What are the differences? What are some advantages or disadvantages? |
Unipolar has 5-6 wires attached. It has two windings on a pole in such that a magnetic north and south created. Current only flows from drive to coils Bipolar has 4 wires attached. Current at stator is reversed during stepping sequence. |
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Read schematic |
Read photo |
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Describe step sequence for uni polar motors? |
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What is motor resolution and what are the torque characteristics? |
It is the number of steps of the motor. It is twice as large in the half-step mode which also has less holding torque. |
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How do you switch electrical polarity in bipolar motor? |
H bridge is used to change the polarity at each phase winding of bipolar motor. Pair of transistors used to switch current direction. |
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Half Stepping for bipolar motors |
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Stepper motor features |
Can rotate in both directions Precise angular movements Hold torque at zero speed Detent torque when not energized Can have large number of step positions Responds to input pulse signals pulse signals pulse signals |
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Uses for stepper motors |
Positioning - 3d printing xy platform and cnc Speed control - robotics Low speed torque - good for low speed high precision movements |
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Limitations for stepper motors |
Low efficiency - takes power even when not turning Low high speed torque No feedback - no sensing for where position is. Need to use other switches etc to tell position. |
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