301. The main function of the controller in a servo system is to?
A) Drive the load directly
B) Generate control signals based on error
C) Supply constant voltage
D) Provide mechanical damping
Ans: B
Explanation: The controller compares reference and feedback signals to produce an error-correcting control signal.
Q302. In a closed-loop servo system, when error becomes zero, the motor?
A) Speeds up
B) Stops
C) Oscillates
D) Reverses
Ans: B
Explanation: When error = 0, the desired and actual positions match, so the motor stops.
Q303. The accuracy of stepper motors is typically in the range of?
A) ±10°
B) ±1°
C) ±5% of step angle
D) ±25% of step angle
Ans: C
Explanation: Stepper motors maintain accuracy typically within ±3–5% of step angle.
Q304. The torque-speed characteristic of a stepper motor is?
A) Linear
B) Drooping
C) Constant
D) Rising
Ans: B
Explanation: As speed increases, torque decreases, giving a drooping characteristic.
Q305. A servo motor can be classified as?
A) AC or DC type
B) Induction or synchronous type only
C) Stepper or reluctance type
D) Switched reluctance only
Ans: A
Explanation: Servo motors may be AC or DC, depending on the control method used.
Q306. Stepper motor speed is directly proportional to?
A) Supply voltage
B) Pulse rate
C) Step angle
D) Load torque
Ans: B
Explanation: Speed = Step angle × Pulse frequency. Increasing pulse rate increases motor speed.
Q307. In servo motors, armature control is used for?
A) Speed control
B) Torque control
C) Position control
D) Temperature control
Ans: A
Explanation: Armature voltage control varies motor speed in DC servo motors.
Q308. Stepper motors are controlled by?
A) Analog signals
B) Digital pulses
C) DC voltage only
D) Frequency signals only
Ans: B
Explanation: Stepper motors move step-by-step in response to digital pulse inputs.
Q309. AC servo motors are often of which type?
A) Squirrel cage induction
B) Two-phase induction type
C) Single-phase synchronous
D) DC commutator type
Ans: B
Explanation: AC servo motors are usually two-phase induction type for smooth control.
Q310. Which of the following reduces resonance in stepper motors?
A) Increasing step angle
B) Microstepping
C) Reducing torque
D) Increasing speed
Ans: B
Explanation: Microstepping smoothens motion and reduces mechanical resonance.
Q311. What type of control system is a stepper motor generally used in?
A) Closed-loop
B) Open-loop
C) Hybrid-loop
D) Feedback-controlled
Ans: B
Explanation: Stepper motors are mostly used in open-loop systems (no feedback).
Q312. The feedback element in a servo motor system provides a signal proportional to?
A) Reference input
B) Output (position or speed)
C) Motor current
D) Error voltage
Ans: B
Explanation: The feedback element senses the actual output for comparison with the reference.
Q313. The torque-to-inertia ratio of a servo motor is usually?
A) Low
B) High
C) Zero
D) Constant
Ans: B
Explanation: High torque-to-inertia ratio ensures rapid acceleration/deceleration in servo motors.
Q314. The main advantage of stepper motors over servo motors is?
A) High speed
B) No feedback required
C) Continuous rotation
D) High power
Ans: B
Explanation: Stepper motors can operate without feedback, simplifying the control system.
Q315. The rotor of a DC servo motor is similar to?
A) Synchronous motor
B) DC motor armature
C) Induction rotor
D) Reluctance rotor
Ans: B
Explanation: DC servo motor rotor has a DC armature with a commutator for control.
Q316. In a stepper motor, full-step operation means?
A) Two phases are energized simultaneously
B) One phase is energized
C) All phases are off
D) Motor runs continuously
Ans: A
Explanation: In full-step mode, two phases are energized to increase torque.
Q317. What determines the direction of rotation in a DC servo motor?
A) Armature current direction
B) Field polarity
C) Input voltage magnitude
D) Encoder feedback
Ans: A
Explanation: The direction of armature current decides the rotation direction.
Q318. Which of these stepper motors provides the highest torque per volume?
A) Variable reluctance
B) Permanent magnet
C) Hybrid
D) None
Ans: C
Explanation: Hybrid stepper motors combine PM and VR features for high torque and precision.
Q319. Servo motors are used in which of the following systems?
A) Conveyor belts
B) Positioning systems
C) Cooling fans
D) Pumps
Ans: B
Explanation: Servo motors are ideal for position control applications like robotics, CNC.
Q320. Stepper motor resolution is defined as?
A) Torque per ampere
B) Steps per revolution
C) Speed per voltage
D) Pulse frequency
Ans: B
Explanation: Resolution = number of steps per revolution; higher steps = better resolution.
Q321. A servo system is stable when?
A) Gain is high
B) Phase margin is zero
C) Error tends to zero
D) Feedback is open
Ans: C
Explanation: Stable systems have minimal steady-state error and bounded response.
Q322. Stepper motor back EMF is proportional to?
A) Step rate
B) Supply voltage
C) Load torque
D) Resistance
Ans: A
Explanation: Back EMF increases with step rate (speed) of rotation.
Q323. The resolution of a 1.8° stepper motor is?
A) 100 steps/rev
B) 200 steps/rev
C) 50 steps/rev
D) 400 steps/rev
Ans: B
Explanation: Resolution = 360° / 1.8° = 200 steps/rev.
Q324. A typical servo amplifier works as a?
A) Power converter
B) Motor driver
C) Feedback comparator
D) All of these
Ans: D
Explanation: A servo amplifier acts as driver, power stage, and comparator for control signals.
Q325. The most significant advantage of microstepping is?
A) Higher torque
B) Reduced vibration and noise
C) Increased speed
D) Simpler control
Ans: B
Explanation: Microstepping minimizes vibration and provides smoother motion.
Q326. Which motor can maintain torque even when stopped?
A) DC motor
B) Induction motor
C) Stepper motor
D) Universal motor
Ans: C
Explanation: Stepper motors can hold position with holding torque when energized.
Q327. AC servo motors usually have how many poles?
A) 2
B) 4
C) 6
D) Many
Ans: A
Explanation: Two-pole AC servo motors offer quick response and low inertia.
Q328. In servo control, derivative control helps in?
A) Reducing steady-state error
B) Improving transient response
C) Increasing overshoot
D) Reducing speed
Ans: B
Explanation: Derivative control anticipates future error, improving transient response.
Q329. Stepper motors are widely used in printers because they?
A) Require high power
B) Provide precise position control
C) Are AC operated
D) Use feedback sensors
Ans: B
Explanation: Stepper motors provide accurate step-based motion ideal for printing mechanisms.
Q330. In a DC servo motor, feedback signal is usually a function of?
A) Armature voltage
B) Motor speed or position
C) Field current
D) Input power
Ans: B
Explanation: Feedback in servo systems corresponds to actual speed or position.
Q331. Which of the following has the smallest step angle?
A) 90°
B) 15°
C) 1.8°
D) 7.5°
Ans: C
Explanation: 1.8° step motors have finer resolution and smoother control.
Q332. The response time of servo systems depends on?
A) Feedback gain
B) Motor inertia
C) Load
D) All of these
Ans: D
Explanation: Response time is affected by system gain, inertia, and load characteristics.
Q333. A hybrid stepper motor combines what characteristics?
A) High torque and high resolution
B) High speed and low torque
C) High efficiency and low cost
D) None
Ans: A
Explanation: Hybrid steppers combine PM and VR features for high torque and fine step size.
Q334. A servo motor control loop includes?
A) Controller, actuator, feedback
B) Amplifier only
C) Load only
D) None
Ans: A
Explanation: A closed-loop servo consists of controller → amplifier → actuator → feedback.
Q335. The step angle can be reduced by?
A) Increasing rotor teeth
B) Reducing stator poles
C) Decreasing supply frequency
D) Increasing current
Ans: A
Explanation: More rotor teeth = smaller step angle = better resolution.
Q336. Stepper motor operation is synchronized with?
A) Load torque
B) Input pulses
C) Supply voltage
D) Frequency
Ans: B
Explanation: Stepper motor rotation synchronizes with input pulse sequence.
Q337. Servo systems provide feedback to correct?
A) Phase delay
B) Output error
C) Supply variation
D) None
Ans: B
Explanation: Feedback continuously corrects output error in servo control.
Q338. Which type of control provides the most accurate servo performance?
A) Open-loop
B) Closed-loop
C) Semi-open loop
D) Manual control
Ans: B
Explanation: Closed-loop control ensures precision and automatic error correction.
Q339. The damping in a servo motor prevents?
A) Oscillation
B) Speed increase
C) Load variation
D) Phase delay
Ans: A
Explanation: Proper damping avoids oscillations around the setpoint.
Q340. Stepper motor current is controlled to?
A) Maintain torque
B) Increase speed
C) Reduce voltage
D) Change polarity
Ans: A
Explanation: Torque is directly proportional to phase current, so it's controlled carefully.
Q341. Which parameter determines servo bandwidth?
A) Motor resistance
B) Control gain and feedback speed
C) Shaft diameter
D) Supply frequency
Ans: B
Explanation: Bandwidth depends on system gain and feedback dynamics.
Q342. The motor that runs on feedback of shaft position is?
A) Stepper motor
B) Servo motor
C) Induction motor
D) DC motor
Ans: B
Explanation: Servo motors use position feedback for precise control.
Q343. The typical speed range of stepper motors is?
A) 10–500 rpm
B) 1000–5000 rpm
C) 5000–10000 rpm
D) 1–5 rpm
Ans: A
Explanation: Stepper motors operate typically between 10 and 500 rpm for stable performance.
Q344. In servo control, integral control action helps in?
A) Reducing steady-state error
B) Increasing overshoot
C) Slowing response
D) Increasing noise
Ans: A
Explanation: Integral control eliminates steady-state error over time.
Q345. The primary cause of missed steps in a stepper motor is?
A) Overloading
B) Undervoltage
C) Low frequency
D) High torque
Ans: A
Explanation: Excessive load torque causes the motor to miss steps and lose synchronization.
Q346. The AC servo motor is mainly designed for?
A) Constant speed
B) Variable speed and position
C) Torque only
D) DC applications
Ans: B
Explanation: AC servo motors control variable speed and position precisely.
Q347. The smallest movement a stepper motor can make is determined by?
A) Step angle
B) Supply voltage
C) Load
D) Damping
Ans: A
Explanation: Step angle defines the minimum angular displacement per pulse.
Q348. A typical DC servo motor has what kind of torque-speed curve?
A) Linear
B) Parabolic
C) Drooping
D) Constant
Ans: A
Explanation: DC servo motors have linear torque-speed characteristics.
Q349. When pulse frequency increases, stepper motor speed?
A) Decreases
B) Increases
C) Becomes constant
D) Stops
Ans: B
Explanation: Speed ∝ Pulse frequency, so more pulses per second → higher speed.
Q350. The servo motor’s output is proportional to?
A) Input voltage
B) Error signal
C) Reference speed
D) Load torque
Ans: B
Explanation: The error signal determines servo motor output (speed/position correction).
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