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Low-inertia motion control system speeds intelligent security barriers

• optical turnstiles achieve opening times of less than half a second

Bristol, UK, March 4th, 2004 ......PathMinder's latest retracting security barriers for controlling pedestrian access to buildings use low-inertia Baldor servo motors with neodymium magnetics to achieve opening times of well under 500 milliseconds. In conjunction with fine control of the drive's control loops and dynamic motion facilitated by the Mint-based software, the barriers offer a combination of speed and smoothness that is setting new standards in the access control industry.

Intelligent sensing is a core driver for Ottawa-based PathMinder, and the OEM has developed a unique infrared beam and pattern recognition system that defeats attempts at unauthorized access such as 'side-by-side' passages (i.e. two people trying to walk through together).

But speed and smoothness of operation are equally critical, to optimise throughput and support productivity enhancements in access tokens such as proximity cards, and to instil confidence that encourages users to speed their passage.

These requirements place performance demands on the underlying motion system, and PathMinder selected a system based on two of Baldor's BSM N-series of brushless rotary servo motors to actuate the barriers, controlled by two of Baldor's Flex+Drive series of drives. The motors' rare-earth neodymium iron boron magnetics - with an inertia figure that is considerably less than standard servo motors using ferrite magnets - provide a responsiveness that speeds barrier actuation. The magnetics additionally help to deliver higher than average torque for the size of motor, a feature that helped PathMinder to install a movement system within the small enclosure that houses 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 dynamic movement was simplified by the drives' Mint motion control language which gave PathMinder high-level commands to optimize 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 dynamically monitor drive current, and if necessary limit it on the fly, so that the parameter could be employed as part of the barriers' triple-redundant safety system that prevents closure on a person.

"The high native speed of the barrier actuation system gives us plenty of leeway at the system level to determine access control rights and open the barrier without slowing pedestrians," says Gennady Reshetnikov of PathMinder.

"Although performance was the key factor in designing this system, the production volumes in this business demand a competitive motion control architecture - a goal that's been greatly aided in this instance by the use of all-in-one intelligent drives - with their built in positioning capability", adds Kris Nair of Baldor's Ontario office, who provided applications support.

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 per minute - which helps avoid queuing. Tall, heavy glass is typically used to offer a strong physical barrier which, 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-a feat possible only with strong, precisely controlled motors.

BACKGROUND INFORMATION
Intelligent drives Baldor's Flex+Drive intelligent servo motor drive for industrial positioning applications features an integrated motion controller compatible with the Mint language. At the heart of the single-axis brushless servo drive is a fast 32-bit DSP-based controller. Each drive includes a 14-bit analog input and 11 digital I/O lines - enough to handle the associated I/O requirements for many simple automation applications. Two of the digital inputs can capture data within a microsecond. This provides the performance required for high-speed adjustments such as those required in registration applications. Flex+Drive offers expansion interfaces that accept low-cost modular plug-ons to configure it for users’ preferred fieldbus communications and position feedback technology. Flex+Drive servo drives will run these programs autonomously, providing a complete standalone solution for machinery and automation - optionally controlling further I/O including man machine interfaces using fieldbus communications. Alternatively, the drive will function as a slave to a PC, for users who want to build automation equipment with sophisticated Windows-based operator interfaces, using Baldor's free Mint ActiveX controls.

Neodymium servo motors Baldor BSM-N Series of brushless servo motors based on rare-earth neodymium iron boron magnets are ideal for for building equipment requiring high acceleration and speeds. The range offers users a wide choice of frame sizes with peak torques as high as 40Nm, and a choice of maximum speeds. BSM-N motors are also available in three lengths with single, dual or triple stacks of magnets, allowing users to match performance characteristics easily against particular application requirements. A rugged brushless resolver is integrated into the motor for simple system building; incremental encoders are available optionally.