Samtec Technology Talk: Connectors in Robot Design

Samtec Technology Talk: Connectors in Robot Design

Keywords: Samtec technology robot connector 

“Robots have been coexisting with human society for decades, and the robots in question are not the cute or futuristic designs that make headlines or make waves at tech conferences. They are the machines that work behind the scenes, responsible for the things we do every day. Many products used in life.”

Abstract/Foreword

Robots have been coexisting with human society for decades, and the robots in question are not the cute or futuristic designs that make headlines or cause a stir at technology conferences. They are the machines that work behind the scenes and are responsible for making many of the products we use in our daily lives.

Problems encountered in robot design

These industrial robots are relatively low-intelligent by today's standards, but they serve an important purpose. They are designed to perform the same tasks repeatedly and with great precision. The automotive industry has been using industrial robots for more than half a century. They perform hazardous or boring jobs such as welding, painting and assembly.

Creating connector solutions for industrial robots can be a headache for manufacturers, with a key consideration being reliability. When we describe a connector, we often use the mating cycle as a key measure of its service life. A mating cycle is defined as the act of mating and unmating a connector, and most manufacturers publish a minimum expected number of mating cycles for each type as a measure of their reliability.

It would not be surprising if the actual performance of the connectors varied significantly when used in the real world. In a clean and comfortable environment, a connector may last far longer than necessary if used correctly by an experienced technician. Conversely, if a connector is used in harsh field conditions and the plug is frequently unplugged in a hurry, the user may find that its service life is much shorter than expected. This is easily the case when we look at the factory floors where industrial robots must perform tasks.

Another issue faced when designing for robots is motion. Robots move quickly, often in multiple directions, for hours or even days. All parts of the robot - its arms and appendages - need to be connected to each other to provide the data, power and signals they need to work. Every moving joint is a problem for the designer.

Design and testing for reliability

When designing for robots, the structure within the connectors they use is core to their performance. Most of us are familiar with connector designs that use terminals arranged in a traditional plug and receptacle arrangement. This has been with us for a long time as it provides one of the best ways to connect two circuits.

The concept of traditional terminal and socket design is that a fixed terminal is inserted into a slightly smaller socket. The socket flexes sufficiently to allow the terminals to enter and create a spring force that ensures contact between the two halves.

One of the advantages of this design is that the pin terminals are relatively easy to manufacture. Terminals can be solid, machined from a solid bar, or hollow, made from flat sheet metal that is rolled or formed into a three-dimensional shape. While different manufacturing techniques have their own advantages, the important point in this case is that the terminals themselves are fixed.

It is the socket terminals that provide the flexible element in the design. The socket is slightly smaller than the pin, so there needs to be some flexibility to accommodate it. As the socket expands to accommodate the pins, it exerts a positive pressure on the pins. This is important to ensure good electrical contact between the mated halves and to reduce the effects of vibration that may occur during normal use.

However, positive spring pressure creates other problems. To overcome the spring resistance, force is required to engage and disengage these terminals, known as insertion force and extraction force respectively. While the force required for a small number of terminals is negligible, the situation changes when we consider a connector with many circuits. In order to successfully mate such a connector, a large amount of force needs to be applied, so the operator must ensure that the connector is properly aligned.

Cable Risks

Cables also present risks when used in industrial robots. When designing for robots, cables need to be protected to ensure they don't bend beyond their built-in limits or twist in a cumbersome way. Even if this could be done, the cable is still made of metal, albeit very fine wires woven together to create a flexible cable. As we have seen many times throughout history, metal fails. The constant movement of the cable itself can weaken the wire, seriously affecting its performance and compromising its reliability, even before the cable physically breaks.

However, with repeated movement, the cable will eventually break, at which point the connector will become extremely important as the cable will need to be removed and replaced. There are some very impressive cables out there that offer a longer working life, just like there are high-reliability connectors. I remember I had a multi-core cable that was so soft it felt like a piece of cooked spaghetti. But eventually, even such cables fail from repeated use.

Perhaps the biggest headache when designing for a robot is the power supply. Modern battery technology is now more capable than ever, thanks in large part to the automotive industry. However, the battery needs to be charged, and until some clever engineer figures out a way to deliver massive amounts of power over a Bluetooth link, the connector is the way to go.

As long as robots continue to evolve, Samtec will continue to come up with new ways to connect them. For the latest products, visit our Industrial Applications page, where we explore the world of industrial automation and autonomous robots.

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