1. Field of The Invention
The present invention relates generally to the field of railway electric-vehicle control systems, and, more particularly, to a positive-feedback go/no-go control system for a railway electric vehicle. Although the present invention is subject to a wide range of applications, it is especially suited for use in a railway electric-vehicle ride at an amusement park, and will be particularly described in that connection.
2. Description of the Related Art
A positive-feedback go/no-go control system for a railway electric vehicle provides motion commands to the electric vehicle, detects the presence of a vehicle on a section of the railway, and provides vehicle-status information.
Conventional railway electric-vehicle control systems are known. Typically, a main controller provides speed command signals to control the speed at which the vehicle is to travel. The command signals are direct-current (DC) voltages of different levels corresponding to the commanded speeds. For example, a 12-volt (V) level is a low-speed command and 24-V level is a medium-speed command.
The vehicle control system usually has two signal lines running parallel to the railway tracks upon which the electric vehicle travels. The signal lines are divided to form sections so that different command signals can be provided to different sections. The signal lines conduct the command signals to the vehicle by way of the vehicle's electrically conductive brushes that contact the signal lines.
A receiving unit on the vehicle discriminates and detects the command speed from the speed command signal. The receiving unit also has a presence-signal load circuit for generating a presence signal that is applied to the signal lines. The presence signal is generated by shunting a resistance between the signal lines, which causes a current to flow between the signal lines of the section that the vehicle is traveling over. The main controller can detect the presence signal and thus determines the presence or absence of a vehicle on a particular section.
Although suitable for some railway electric vehicles, such a control system does not provide a signal from the electric vehicle to the main controller that indicates the vehicle's intended action. Thus, in this conventional control system, the main controller cannot ascertain whether the vehicle is responding as desired or is malfunctioning.
Other schemes for the encoding the command signal are known. In a control system for a model train, the vehicle direction is controlled by the polarity of the power source, and the vehicle speed is controlled by the intensity of the power source supplying power to the train's motor.
In a known control system for a railway electric-vehicle ride at an amusement park, the encoding of the signal is pulse-width modulation. The command signal is applied to a signal line known as an outbus by a wayside controller. The presence of a 24-V signal and its pulse width indicates whether the command is "stop," "park," or "run." A 0-V command signal (no pulse) represents "stop."
The 24-V pulse passes through a vehicle-based shunt element and results in an 18-V presence signal applied to a signal line known as an inbus. The positive voltage on the inbus indicates to the wayside controller that the ride vehicle is present in a particular section or zone. If no vehicle is present in the zone, then no voltage is applied to the inbus. The lack of voltage on the inbus indicates to the wayside controller that no vehicle is present in the zone.
The wayside controller and electric vehicle also communicate by radio-frequency (r-f) signals for monitoring the ride vehicle's status. Alternatively, other forms of communication, for example, modulation of the command signal, may be utilized.
Although suitable for some railway electric vehicles, such a control system does not have the ability to detect vehicle presence when the command signal is 0 V. Further, noise is generated on the control bus bars by high-power switching, capacitive and inductive coupling with power busses that supply motive power to the electric vehicle, and brush bounce. This noise can corrupt the command signal and provide an erroneous command to the vehicle. Filtering and other techniques can resolve this situation, however, they add to the expense of the system.
Moreover, although this control system provides vehicle status information to the wayside controller, it does so with the addition of relatively expensive r-f equipment. Furthermore, if modulation of the command signal is employed to provides vehicle status information, it is subject to similar noise problems as does the command signal.
A need therefore exists for a positive-feedback go/no-go control system that reliably communicates motion commands, vehicle-presence signals, and vehicle-status signals in the presence of high electrical noise and does so without the addition of expensive add-on equipment.