ITPEC FE Morning October 2019 Question 4
A vehicle travels along a circle in the figure below. Two sensors L and R are attached to the left and right rear wheels, whose revolution speeds are independently controlled. Sensors L and R are photo reflective sensors, whose 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 for ensuring that the vehicle travels along the black outline of the circle? Here, if the values of the two sensors match, the revolution speeds of the motors return to the initial 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 (b)
Why not others:
- •(a) — turns right in both cases, so the vehicle leaves the line whenever it shifts to the left
- •(c) — 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 left in both cases, so the vehicle leaves the line whenever it shifts to the right
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
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official FE past-paper collection or Report an issue.