Question – For a school project, I am looking at roller coaster control systems. If you could answer my questions, I would really appreciate it. Does the current system of monitoring roller coaster trains with photo eye sensors and proximity sensors have any limitations? Could it be potentially safer if the exact position of the roller coaster trains where known at all times instead of only knowing when the roller coaster trains passed through a photo eye sensor?
The history of control circuits on rails goes back about 150 years. See the Wikipedia “track circuit” article.
Some ride systems do use continuous position monitoring, typically using either absolute (curvi) linear position encoders, relative encoders, or a combination of technologies. Two sensing systems are usual for safety, preferably of different types (and therefore different failure modes). Encoders provide the high quality feedback signal necessary to enable close “servo” control of position and speed.
The proxes and photo eyes that you mention do indeed have limitations, notably their resolution. Block systems work by only admitting vehicles past a stop point (brake or brake-motor) if the system can confirm that there are no vehicles in the block between this stop point and the next point (or multiple points). Both technologies have limits: eyes sense segments of track about as long as the train, proximity sensors sense over the length of the fin or other flag. Multiple proxes can be used to obtain finer position data (see Quadrature), but most often simpler arrangements are more reliable and safer. As gravity coasters have few places where the train can be stopped, not many sensors are needed. A simple four-zone, 2-train system may only have a couple dozen sensors, including those used for decel and parking. However, a twelve vehicle system may have hundreds of sensors to provide the necessary granularity of sensing, particularly in the station where vehicles are close together. Requirements go up with rising capacity and lower dispatch interval.
Finally, “safe” is determined by analysis, not just by choosing one superior technology or technique. Multiple layers of techniques are typical. For example: a new tech like continuous position sensing may be used together with older proven tech like prox sensors.