When you walk past a robotic welding system in an automotive plant, the first thing you probably notice is the robot’s arm. What often goes unnoticed, however, is the multitude of signals exchanged between sensors, controllers, and actuators every millisecond.
Even a slight delay can be enough to cause the final weld seam to deviate from the target by several millimeters. This is precisely why industrial communication is often an invisible discipline that only becomes visible when it fails.
Communication is Crucial in Robotics
A six-axis robot arm is, first and foremost, an expensive piece of technology that only transforms into a machine when it receives the information necessary for its operation.
Encoders are then able to report joint angles, force sensors detect contact pressure, and cameras verify whether a workpiece is actually in the position specified by the program. All of this happens in a matter of milliseconds.
The controller then combines the measured values, recalculates the robot’s movement, and sends updated commands to the actuators before the next cycle begins.
But how small are the tolerances in practice? After all, in high-speed pick-and-place applications, even a delay of two milliseconds can lead to major problems.
Teams that underestimate the importance of fine-tuning this chain usually have to deal with the often unpleasant consequences during commissioning, namely when a correction costs significantly more than originally planned and estimated.
Physical connectors as fundamental elements of automation
While protocols often take center stage in technical discussions, the physical connection between the devices used deserves equal attention. Cables running through a robot cell undergo millions of bending cycles, while coolant splashes, temperature fluctuations, and metal dust attack the housings. A standard connector would therefore wear out within a few weeks.
To avoid such problems, the industry uses circular connectors with screw locking mechanisms. With an IP69K protection rating, they ensure the contacts remain sealed even when a cell between layers is cleaned at high pressure.
Of the most common sizes, M12 connectors are the most widely used for wiring sensors and actuators in factories. An M12 housing covers Ethernet, power, and signal via different pin assignments, allowing a single connector family to power an entire machine. In compact grippers or confined articulated housings, where every millimeter counts, engineers instead opt for M8 or M5 connectors.
Choosing the correct coding for each cable run may seem pedantic at first. However, even seemingly minor errors can cause problems for experienced teams. Mixing up power and data connectors is just one example of the common commissioning errors.
Key Components of a Robot’s Communication System
Sensors and Signals
Most industrial robots use multiple sensors simultaneously, including:
- Encoders for position and speed measurement
- Force-torque sensors for resistance measurement during tool contact
- Image processing systems for verifying the workpiece’s position and orientation
Some of these sensors still provide analog voltage signals, but digital interfaces are now standard for new installations. They are less susceptible to electrical interference, which is a crucial factor in a production hall with frequency converters and welding equipment.
Communication Protocols
Sensor data and machine commands are transmitted via standardized fieldbus and Ethernet-based protocols. PROFINET and EtherNet/IP enable real-time data exchange between robots, PLCs, and peripheral devices. IO-Link operates at a lower level, connecting individual sensors to the network and eliminating the need for a separate cable for each device.
Furthermore, the differences between robot manufacturers are decreasing. The OPC Robotics Companion Specification, for example, developed jointly by the VDMA and the OPC Foundation, provides industrial robots with a common interface to the Industrial Internet of Things (IIoT). The International Federation of Robotics considers this one of the most important connectivity trends in robotics.
From Components to Complete Systems
To grasp the overall picture, it’s helpful to trace a single signal through a typical production line. For example: A proximity sensor detects an incoming workpiece. The measured value is transmitted via an M12 cable to an I/O module.
This module then forwards it to the central controller via PROFINET. The controller responds with the corrected actuator position for the arm, and the entire control loop closes in less than five milliseconds.
Anyone planning a production cell can use this process as a checklist, noting the respective signal from each cable, adjusting the connector coding accordingly, and verifying that the controller expects the same data.
Factories that view their production chain as a system experience fewer unplanned downtimes. This same process-oriented thinking characterizes manufacturing engineering, where the reliability of an entire production line is more important than the specifications of a single machine.