Development Of Auto-barrier Control System Based On Torque Motor

A auto-barrier (also known as access toll gate) is one of the auto-control units which is based on the combination of the torque motor and vehicle loop detection technology. Recently, it has been widely used in parking lots, toll booths, security areas, access road, and so on.Torque motors are designed to provide high starting torque and sloping characteristics (torque is highest at zero speed and decreases steadily with increasing speed), and operate over a wide speed range. The torque generated by the torque motor changes approximately proportionally to the square of the voltage. This character is commonly used to control voltage by phase control using thyristors or silicon-controlled rectifiers (SCRs). When the voltage supplied to the motors is changed, speed-torque curves with a sloping characteristics shifts to that of the corresponding voltage. So, all kinds of barrier’s movement mode can be achieved.One kind of precise speed/position counters replacing the traditional mechanical limit switch is normally coupled to the shaft of the motor and provide a count to a microprocessor. The upper and lower limits are programmed into the microprocessor .As the access barrier cycles, the counter update the count to the microprocessor. Once the proper count is reached, the access barrier stops smoothly and free of metal fatigue or corrosion. Method of successive approximation is applied in self-optimization of the barrier’s adjustment.In engineering, vehicle loop detectors use a coil of wire buried in the drive way which is connected to an inductive loop detector. When a vehicle enters the loop the body and frame provide a conductive path for the magnetic field; causing a loading effect, which in turn causes the loop inductance to decrease. The decreased inductance causes the resonant frequency to increase from the nominal value. If the frequency change exceeds the threshold set by the sensitivity setting, the detector module will output a detect signal. Automatic functioning of the barrier ,such as the barrier will only close when a vehicle passed through the loop ,and the boom will be raised again when a vehicle be detected during the boom fallen time, can be achieved when the loop detector combined with the barrier control unit.According to the requirement of high speed automatic barrier used in ETC system, preliminary study on the combination of the brushless DC motor with its intelligent control mechanism has also been carried on in our task.In our task, we study the auto-control of torque motor in the access barrier, self-optimization adjustment, the theory of vehicle loop detection and its application, etc. and also we provide unique technology to improve operation performance of access barrier used in the field of ETC system. It must be helpful to solve problems on access barrier control, maintenance and fix, and application. It will also be of great value for reference for the development and research of auto-control system of access barrier.