Elevator hoistways extend from an upper terminal landing to a lower terminal landing. Below the lower terminal landing there is a buffer, which may be comprised of springs, oil dampers or both. Elevator safety codes require that the speed of the elevator be checked as it approaches a terminal landing to ensure that the speed can be reduced to a reasonable safe speed should the elevator not come to a normal stop at the landing, but crash into the top of the hoistway or the buffer at the bottom of the hoistway. To see if the elevator is slowing down properly, switches are used to sense the position of the elevator in the hoistway to indicate a point in time when the speed of the elevator should be checked, to be sure it is slowing down. In some cases, the switches are mounted on the elevator car and are engaged by cams mounted on the guide rails; in other cases, the cam is mounted on the elevator car and various switches are mounted on the guide rails. In either case, the switches normally are operated by rotating arms which have a roller on the end, the roller engaging the cam surface.
In all of these cases, the installation of the cams or switches in the hoistway is quite costly. The hoistway switches and cams need significant maintenance. Unacceptable noise is generated when rollers engage the cams and the contacts open and close. As elevator speeds increase (such as up to 10 meters per second), the mechanical forces result in the switch equipment having to be stronger, making more noise, and requiring more frequent replacement.