2 System Challenges to Understand When Changing Communication Interface

Complex systems like robots have several communication interfaces – and potentially a mix of different interfaces – to support because of different subsystem requirements. Figure 2-1 shows a decentralized robot system with several communication interface paths, each of which has a different specification.

Changing to SPE from these interfaces provides benefits for the overall system cost and mechanical dimensioning. However, SPE also creates the need to make sure that the necessary timing performance is possible.

The green lines in Figure 2-1 show the communication interface, which usually employs a real-time protocol that makes sure deterministic communication with a high data rate for amount of data transferred. The blue lines show the motor drive encoder interface, which is typically accomplished with either a proprietary digital protocol based on RS-485, or an analog encoder interface.

The internal communication path of a robot operates in proximity to the location of switching phases of the motors. This implementation can reduce the number of cables and power levels in the robot, while also eliminating the need for cooling at the robot joint. However, moving the placement of power electronics into the manipulator has the potential to cause continuous noise in the communication interface of the system. This in turn creates a new challenge of losing communicated data due to the poor noise performance of the chosen interface or design. In SPE, performance in noisy environments is highly dependent on the type of PHY decoupling selected. Section 4 explains galvanic and capacitive decoupling. As previously described, another challenge is that the manipulator is constantly moving the cable around, damaging the cable over time.

Battery-driven robots also benefit from reducing the number of cables with SPE, since doing so reduces weight, increases system efficiency and so maximizes time between charges (extends battery life).