Push-pull connectors are simply connectors that lock, providing a secure mating system in mission-critical applications. According to Steven Lassen, products & applications manager for LEMO USA Inc., they only require an axial force to engage and disengage, thus do not need a rotational force.
Common applications include medical devices and equipment, military use on both vehicles and on-soldier devices, instrumentation and any application where an accidental disconnection can be catastrophic and dangerous. They are used externally on equipment that requires connectors to be cycled many times over the machine or system’s lifespan. Push-pull connectors are designed to have a minimum of 2,000 mating cycles for plastic versions and 5,000 mating cycles for metal versions. Even after these high numbers of mating cycles, the contact resistance increase is only a few milli-ohms in most cases, said Lassen.
Most push-pull connectors are lightweight and can be made of plastics or metals, but they are rugged, offering thousands of mating cycles. Because of the locking mechanism, they also provide a clean, streamlined look on devices. They also offer space-saving benefits, as they only require two fingers to grip the shell to connect or disconnect, without twisting. Multiple connectors can be mounted closely together and don’t require bulky tools for connection and disconnection.
Invented by LEMO, the locking mechanism on a push-pull connector can only be released by squeezing the connector body or pulling back on an outer sleeve to unlatch. Locking is done simply by pushing the plug into the receptacle. This prevents accidental disconnects.
The locking mechanism is based on a plug with an inner sleeve that has latches that are held in place by an outer sleeve. “When locking (mating), the plug’s inner sleeve latches retract and slide along the inside of the mating receptacle until reaching a groove with a matching profile of the latches. At that point the latches snap into the receptacle groove’s profile and lock the connector in place,” Lassen said. “When unlocking (de-mating), pulling the outer sleeve moves the latches away from the profile groove and allows the plug to be easily removed.”
Although there are some square and rectangular designs, most industrial-strength push-pull connectors are circular, allowing for more complex cable assemblies. In addition, one of the most cost-effective methods for making a part with demanding high tolerance is by machining circular bar stock. Most of the internal components are circular as well, such as the contacts, insulator, spacers, collets and collet nuts. Rectangular designs have latches on the sides, but still can use some of the same inner circular components.
Push-pull connectors can be used to transfer power, data, signal, fiber optics, thermocouple, or fluidic/pneumatic media. Hybrids allow users to combine two or more types into a single cable to simplify use and better organize or make foolproof cabling for the end user. Most circular push-pull connectors are designed for use with circular cables, so it is also important in the cable design to add appropriate fillers, especially in an application requiring environmental sealing.
Some push-pull connectors are designed as disposable devices for use in applications where cleanliness is critical. They can be designed for indoor and harsh outdoor applications. Key characteristics can include waterproof ratings (IP68) for complete submersion in water, dust-proof, vibration and shock resistance and more.
Finally, it is important to understand that push-pull connectors can be uniquely keyed to allow only the desired pair to operate. Standard or reverse gender contacts can be used in their design, depending on which end of the cable power is coming from. In metal connectors the shield is carried through the shell to maintain 360° continuity and EMI protection.
See an animation of a push-pull connector in action at LEMO USA’s website, www.lemo.com.