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With the adoption of ASME A17.1, the requirement for elevator door-locking systems became virtually mandatory for most door operators. As manufacturers and building owners have scrambled to meet these requirements, they’ve discovered that every approach available presents significant drawbacks and compromises. However, Electrodyn Systems, Ltd., a leader in aftermarket solutions, has now introduced the Electrolock.
The Importance of Door Restrictors
In the world of vertical transportation, safety is paramount. To ensure passenger well being and to comply with regulations, elevator manufacturers have devised various types of door-locking systems known as “door restrictors.” These devices ensure that if an elevator stalls during operation between floors, onboard passengers cannot force the door open and enter the hoistway. Restrictors also protect elevators against door misuse and related acts of vandalism. Industry experts and rescue personnel agree that the safest place for passengers is inside the elevator, and door restrictors minimize liability and the risk of injuries or fatalities.
A Challenge to Manufacturers
To meet the requirement for door security, manufacturers have explored two different approaches to restrictor design: mechanical and electromagnetic. Each has its strengths and weaknesses. Principally, mechanical solutions rely on some part of the elevator cab to make physical contact with every landing to activate and deactivate a locking bar. Electromagnetic solutions generally employ some arrangement of photoelectric eyes, reflective tape and/or steel targets at landing areas to activate a solenoiddriven locking bolt.
Mechanical technology would seem attractive, since it operates by momentum and not electricity. In the field, however, technicians have found that calibration of such mechanisms requires frequent adjustment to the car and hoistway doors – a problem that expands with the number of landings and cars at a given site. Also, these devices are notoriously noisy and difficult to repair.
Electromagnetic devices aimed to solve the problems of mechanical door restrictors by employing beams of light instead of metal-to-metal contact. In order to operate properly in the event of a power failure, these types of locks require backup battery power. Unfortunately, in the event of battery failure, the locks will not necessarily remain in the correct position, thus rendering these systems as not code-compliant. Moreover, by requiring continuous power, the locking plunger solenoids used by these systems are prone to coil burnout, and the photoelectric eyes are vulnerable to dirt, dust and the presence of ambient light such as that found in exposed hoistway settings.
In Search of a Better Design
James Marinelli, CEO of Electrodyn Systems, knew that there had to be a solution to the problems posed by existing door restrictors. “Our clients and technicians were outspoken in their desire for a fail-safe restrictor that would be reliable, cost-effective and maintenance-free,” he noted. “And it would have to be code-compliant as well.”
Marinelli carefully studied the various models of restrictors in use, noting which features were effective (and which ones were not). “The key problem,” he decided, was “reliability.” In Marinelli’s opinion, lives are too important to trust to batteries, and no door restrictor should be able to fail in an unsafe position. The first breakthrough in his analysis was the application of radio frequency identification (RFID) technology as the interface between the locking mechanism and the landing position indicator, a device the company calls an electrosensor .
“With RFID,” Marinelli explained, “the lock always recognizes the electrosensor, no matter what.” In testing, his team discovered that the electrosensors could be covered in dirt, oil and grime – typical of hoistway hazards – with no effect on the system. He added, “The locks continued to function correctly even when we covered the reader’s head with our hand.”
Next to be solved was the problem of current. Regular solenoids can change their state when power is interrupted, which is why photoelectric systems require battery backups. And solenoids are prone to buzzing and eventual coil burnout. Marinelli worked with a specialty solenoid manufacturer to devise a bi-stable solenoid that operates with pulsed microbursts of electricity. “We solved two problems at once,” Marinelli noted. “The solenoid contains a permanent magnet so that it remains in state until it receives an input.” Moreover, the use of pulse technology protects the solenoid from burnout and ensures a dramatically extended lifespan.
Electrolock – A Total Solution
The combination of the solenoid and its permanently lubricated locking plunger is housed in a sturdy steel enclosure, a device the company calls a magnalatch. Once the team devised a virtually indestructible PVC case for the RFID reader, the Electrolock was ready to meet the elevator world. “Our restrictor was now fail-safe, codecompliant and designed to industrial-strength standards,” Marinelli remarked, “but we added two more important features.” The first is an LED indicator on the power board. The light assists a technician during electrosensor installation by providing an indication of when the electrosensor is aligned to the reader head. The second feature, called doorsaver, is an extra set of dry contacts rated at five amps. Electrolock users can opt to have the doorsaver wired in line with a door operator’s “door open” limit. This arrangement disables the door motor when the magnalatch is in place. Marinelli explained: “Occasionally, a door operator will malfunction and attempt to open the door while a restrictor is in place. In that tug-of-war, the door motor always loses, and the owner faces a costly replacement.”
An Easy Choice Competitively priced with other door restrictors on the market, Electrolock installs in roughly half the time required by a photoelectric system. Because it eliminates the need for expensive (and non-compliant) trickle-feed batteries and is protected from solenoid burnout, it requires virtually no maintenance whatsoever, becoming the industry’s first “set-it-and-forget-it” solution. What’s more, unlike systems using trouble-prone and delicate optics, Electrolock employs solid RFID technology, immune to the harshest hoistway conditions. You don’t have to be a designer or an engineer to know that simplicity means dependability, and these are the qualities you want in a door restrictor.
For more information, check out Electrodyn Systems’s website at www.electrodyn.com.
James Marinelli, head of Electrodyn Systems and inventor of the Electrolock, has worked in the elevator industry since 1965. After spending 22 years in the field, he launched his own firm that has been refitting elevators for the past 18 years. The famous “Red Box,” a fire service retrofit kit, is the company’s footprint and can be found in thousands of machine rooms across