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Low inertia motion control system

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article image PathMinder’s security barriers

PATHMINDER'S retracting security barriers use low-inertia Australian Baldor servo motors with neodymium magnetics to achieve opening times of well under 500ms.

In conjunction with fine control of the drive's control loops, the barriers offer speed and smoothness. The system uses an infrared beam and pattern recognition system that defeats attempts at unauthorised access.

Speed and smoothness of operation are critical to optimising throughput and supporting productivity enhancements. These requirements place performance demands on the underlying motion system. PathMinder selected a system based on two of Baldor's BSM N-series of brushless rotary servo motors to actuate the barriers.

These are controlled by two of Baldor's Flex+Drive series of drives. The motors' rare-earth neodymium iron boron magnetics provide a responsiveness that speeds barrier actuation. They have an inertia figure that is considerably less than standard servo motors using ferrite magnets.

The magnetics help to deliver higher than average torque for the size of motor. This feature helped PathMinder install a movement system within the small enclosure housing the retracting barriers that is capable of supporting a 100% duty cycle.

PathMinder's need for compactness was aided by the selection of Baldor's Flex+Drive controls, which integrate all the normal features of a servo drive with a programmable motion controller and I/O. Smooth movement was simplified by the drives' Mint motion control language.

This gave PathMinder high-level commands to optimise the movement profile for the application and fine-tune the drive's real-time current, speed and position parameters. An additional attraction for PathMinder was Mint's ability to monitor drive current and if necessary limit it on the fly. This meant that the parameter could be employed as part of the barriers' triple-redundant safety system that prevents closure on a person.

PathMinder's turnstile designs offer a combination of speed, security and safety. Fast barrier retraction contributes to a real-world traffic throughput of 30 people a minute. This helps to avoid queuing.

Tall, heavy glass is typically used to offer a strong physical barrier. This, combined with PathMinder's optical detection matrix, offers excellent security. Three independent safety sensors are utilised to stop the barrier before making contact with a person. This is possible only with strong, precisely controlled motors.

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