ITPEC FE Subject A April 2025 Question 4

Topic: HardwareAlso asked in October 2019

A vehicle travels along a circular path as shown in the figure below. Two sensors, L and R, whose revolution speeds are independently controlled, are attached to the left and right rear wheels. Sensors L and R are photo-reflective sensors, and their values change according to the ratio of black and white regions they pass over. If the ratio increases, the sensor value decreases, and if the ratio decreases, the sensor value increases. Which of the following is an appropriate control to ensure that the vehicle travels along the black outline of the circle? Here, if the values of the two sensors are equal, the motor revolution speeds return to the initial values.

ControlunitMovingdirectionSensor LSensor RFront wheelRear wheelsMotor LMotor RCircle
Sensor L value > Sensor R valueSensor L value < Sensor R value
OptionMotor LRevolution speedMotor RRevolution speedMotor LRevolution speedMotor RRevolution speed

Explanation

Motor L up and R down when L > R; L down and R up when L < R — the vehicle must turn toward the sensor that sees more black.

Each sensor sits over one edge of the black line. More black under a sensor lowers its value, more white raises it. A vehicle turns toward the side of its slower rear wheel.

  • •Sensor L value > Sensor R value: L sees more white and R more black, so the line has shifted to the vehicle's right. Turn right: increase Motor L, decrease Motor R.
  • •Sensor L value < Sensor R value: the line has shifted to the left. Turn left: decrease Motor L, increase Motor R.

Answer (c)

Why not others:

  • •(a) — turns left in both cases, so the vehicle leaves the line whenever it shifts to the right
  • •(b) — turns left when the line is on the right and right when it is on the left, steering away from the line every time
  • •(d) — turns right in both cases, so the vehicle leaves the line whenever it shifts to the left

Key rule: In a two-sensor line follower, speed up the wheel on the side whose sensor sees more white, so the vehicle turns toward the darker sensor and recentres on the line.

Hardware · AI-written, may contain errors

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