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18 Cards in this Set
- Front
- Back
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What is backlash/ when does it take place? |
When changing direction, the driving side exhibits motion while the driven side is stationary - like small amount if slip. Nonlinear in nature |
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How does backlash influence control performance? |
Problems for high precision/repetitive control. Not considered in closed loop systems Nonlinear therefore difficult to compensate using linear control methods |
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How to compensate for backlash? |
PID controller sensor on output side Open loop software compensation Mechanical compensation - spring engage |
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What are two types of AC motors? |
Synchronous AC motors - single phase Asynchronous induction AC Motors - three phase |
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How do AC motors work with slip rings? |
Current flows through wire perpendicular to magnetic field which will cause half rotation according to lorentz rule. Once current is switch to other direction, it will then rotate the other half making 1 full rotation per sine wave. |
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What are slip rings? |
Sliding contacts like brushes in DC motors |
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How do you get rid of slip rings? |
Supply stator with AC supply instead of rotor. Rotor is made from permanent magnets. Attraction and repulsion caude rotation. |
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Characteristics of synchronous motors? |
Speed = system frequency Rotates at constant speed for any allowed torque. Can be used as a generator Use permanent magnets or electromagnets in rotor Needs start motor or squirrel cage to begin rotation |
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Induction motor characteristics? |
Rotor can be squirrel cage or wound rotor No starter motor needed Easy to maintain Simple design Inexpensive High power to weight ratio No power is supplied to the rotor itself |
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Why do induction motors never run at synchronous speeds? |
It runs slightly slower than synchronous speeds because no current would be induced in rotor if it did. Speed is called base speed Slip = synchronous speed - base speed |
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How does the magnetic field in a single phase motor work? Attributes of A single phase motor |
Magnetic field will have fluctuating strength with an ac supply input. The direction is constant but it switches sign and magnitude which enables rotation. Magnetic force applied is not smooth Issue if using large currents or forces Not self starting |
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Attributes of three phase motor? |
Magnetic field is constantly rotatingwith frequency of w Smooth transition of magnetic force around rotor Better performance for large current and loads Self starting |
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How is speed altered in a three phase motor? |
The frequency needs to be changed according to speed desired. The three phases of current go through a bridge rectifier using 6 diodes and creates a dc voltage. This dc voltage goes through a series of igbts/ transistors which are controlled via pwm to create a sine wave of the desired frequency. |
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When to use an AC motor? What are some applications examples? |
High power requirements Complex control profiles Load demand - high duty cycle, efficiency, reliability Large cranes, belts and conveyors |
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Ac motor advantages over dc motor? |
No real maintenance requirements - its okay to put motor out of reach as it doesnt need servicing Small, lighter, less expensive, common Better for high speed, high power applications Load can vary for prelonged periods without any problems, while dc motor brushes and commutators will wear out. |
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What are some advantages for DC motors over AC motors? |
DC are less complex with single power conversion AC to DC Able to produce very high starting accelerating torque (more than 400%) Easily adjustable speed for different uses Available with tachometer and encoders Quieter than some AC motors |
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How does a linear motor work? |
Has an "unrolled" stator, instead of rotation, linear movement along stator is produced. Force is produced by moving linear magnetic field acting in conductors in the magnetic field. |
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Advantages of linear motors? |
High accuracy Fast time response No backlash |
