ABBs ACS880 moves bridges by replacing hydraulics and DC drives
Low voltage AC drives are increasingly being used on a variety of movable bridges, either as part of a new build or as part of a renovation program and tend to replace hydraulic drives or DC drives operating with DC motors.
At the heart of bridge control systems are AC drives that feed power to the electric motors which drive the span or deck of the bridge and control the bridge’s mechanical disk or drum brake. The drives control the speed of the electric motors that are used to either lift or turn the deck around its axis.
The ABB ACS880 industrial drives range provides smooth, stepless, variable speed and torque control for motors used on movable bridges over a wide range of operating speeds and loading. The drive features the motor control platform, direct torque control (DTC), which allows accurate control of speed and torque with or without pulse encoder feedback from the motor shaft. Within bridge applications there are two common master-follower control methods:
– Master speed, with follower in torque control mode:
If two motors are connected to each other via a mechanical shaft, for instance when two motors are lifting opposite sides of a bridge at the same time, then the master drive is speed controlled. This determines how fast the bridge raises or lowers. The follower is torque controlled which results in the load being shared exactly between the master and follower.
– Master speed, with follower in synchro control mode:
If two motors are not connected to each other, such as when the bridge is designed for each motor to work independently in raising or lowering the bridge, yet at the same time, then the master is speed controlled. This determines how fast the bridge raises or lowers. In this instance, the follower is operated in synchro mode to enable symmetrical lifting. This means that the two parts of the bridge are synchronized to lift at same time and at the same angle.
Electric motor mechanical brake control and torque memory
The control program features an integrated brake control logic which in turn utilizes torque memory and pre-magnetizing to open and close the mechanical brake safely and reliably. Alternatively both can be used at same time for additional safety. The brake control logic within the drive includes a function which enables the drive to hold the shaft stationery until the mechanical brake takes over.
The ‘slow down’ safety control function limits the speed to a pre-set level in critical zones. High and low limit sensors stop the drive at the end positions. The ‘fast stop’ safety control function is used in emergency situations.
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