How to Specify Nano D Connectors
Opportunities for small, affordable robots are burgeoning throughout sectors like manufacturing, distribution, security, healthcare, and the home. Cost-effective, teachable, collaborative robots can now work safely alongside people in factories or packaging areas, mobile robots are taking on burdensome fetching and carrying tasks in distribution centres, and roving or airborne robots could soon be handling deliveries autonomously. In healthcare, robotic technologies are harnessed for remote surgery, and to control prosthetic limbs. Homeowners are already coexisting with small robots that handle the vacuuming and lawnmowing, while the advent of home digital assistants could lead on to even more sophisticated robotic home-help in the future.
We know that the availability of increasingly powerful processor ICs, at lower prices with each new generation thanks to Moore’s law, is a major factor aiding the emergence of affordable, flexible robotics. But as these gains allow the machines to become smaller, higher performing, more dextrous, and mobile, hardware such as cabling and connectors must meet more exacting specifications.
Size, Weight and More
Nano-D connectors are widely used by today’s agile robots. Manufacturers can offer versatile products that are small, lightweight, and offer good security and robustness. Close pin spacing of 0.64mm and various configurations allow engineers to choose multi-way connectors from just a few pins to more than 60, in low-height single-row or narrow-width dual-row form factors. There is also typically a versatile selection of board-mounting or flex-circuit mounting connectors, panel-mount, cable-to-board, cable-to-cable, and various other mounting options like vertical or straight tails and surface-mount or through-hole soldering.
Although there is plenty of choice in terms of configurations, equipment designers need to consider how the environment and normal operation of the robot can place extra demands on connectors. There can be extremes of temperature or rapid hot/cold cycling. Mobile robots can experience harsh mechanical shocks and vibration, high resistance to corrosion, or mild oxidation can be important if the robot could be exposed to harsh chemicals or if extremely high reliability is required, such as in medical equipment.
While considering the effects of any of these influences, engineers also need to bear in mind that ordering standard off-the-shelf components is usually more economical and offers faster turnaround than developing a special or custom connector specification. It is important to look carefully at all aspects of the connector, such as the design of the pin-and-socket system and the quality of the nickel or gold plating on the contacts, therefore ensuring the chosen standard components will deliver long-term performance and reliability.
Standard, High-Performance Design
As an example, the pins of Omnetics Nano-D / Bi-Lobe® connectors are made from beryllium copper at 17200 ksi and tempered for continuous spring force. In addition, the spring pin is tapered and shaped to maintain four continuous points of contact. This design, which features an open end, is extremely strong and long-lasting, and allows greater travel in compression and expansion. This ensures continuous electrical contact under operating conditions that can cause other designs to suffer intermittent discontinuities. In high-vibration environments, some connectors allow 10ns open-circuit time, while the spring-pin design of the Nano-D / Bi-Lobe connectors has exhibited zero opens under vibration testing.
The sockets are copper alloy, which expand when the connector is hot and are designed to increase contact pressure; when the connector is cold, the socket contracts and the spring ends close but avoid placing excess stress on the spring and so prolong the connector lifetime. The open-end spring pin exceeds 2000 mates/de-mates in rugged testing.
To ensure long life, the contacts are gold-plated after forming, according to the ASTM B488 Type II specification for electrodeposited gold coatings. Each surface has 50 microinches of nickel and 50 microinches of gold that is controlled using X-Ray Fluorescence (XRF) measurement and checked for non-porous surfaces.
Other important factors to consider are the ruggedness of the connector shell. Low-cost connectors with plastic shells can allow new equipment to be delivered to market at a more competitive price, which is important as the field of robotics becomes increasingly commercialised. On the other hand, in some environments, connectors with plastic shells can become brittle and difficult to lock after re-mating. Omnetics offers a choice of metal shells, including lightweight aluminium plated or anodised shells, stainless steel, or titanium. These are suitable for demanding environments, including in airborne robots or surgical equipment, and can withstand levels of shock and vibration well beyond many of the heavier and larger connector designs.
High retention force, when mated, is another important strength of standard Nano-D connectors. Of course, much of this comes from the integrated jack screws. Recently, Omnetics announced a new latching version of its Nano-D / Bi-Lobe connectors, which allows rapid assembly without tools. The connectors pass the stringent shock and vibration requirements of MIL-DTL32139, which assures rugged service in most any type of robotic equipment, including UAVs or their roving counterparts, UGVs (Unmanned Ground Vehicles).
Advancing into New Environments
However, although a broad selection of robust, standard connectors is available, the robotics industry is developing and moving into new areas so quickly, that some applications may demand special connectors. One example is in security-oriented robotics, which may need surveillance-grade packaging and cabling to prevent deliberate disruption or severing of connections. In these cases, Omnetics can work with customers’ engineering teams to help define the connector requirements and quickly deliver a suitable solution.
The author Bob Stanton is the Director of Technology at Omnetics Connector Corporation.