Automation, assembly lines and robots are nothing new in industry, nor is the implementation of safety functions in safety-relevant applications. As far as the latter is concerned, the 'emergency stop' mode is usually the first choice. This is either activated manually or triggered by additional or correspondingly cost-intensive auxiliary systems such as light barriers or video cameras. Once the fault has been rectified, the assembly line or production robot must be completely restarted, which usually results in longer delays.

The 'Safe Motion Module' (yellow) is located in the Somanet node between the sensor/actuator interface board and the processor board.

© Synapticon

EN 61800-5-2 also provides a systematic method for identifying the safety function. It therefore defines the various 'Safe Motion Modes' and divides safety functions into 'Stop Functions', 'Safe Motion Functions' and 'Safe Brake Functions'.

With this in mind, Synapticon has set out to integrate such safe motion functions directly into decentralized servo controllers for the first time. Until now, this was only possible with safety PLCs, which implement these functions centrally and with additional hardware. The result is embedded safety modules that are integrated decentrally into the controller on each axis.

To understand: A servo drive, which is realized with the so-called Somanet modules from Synapticon, consists of three modules: communication module (Com), processor module (Core) and drive module (Drive). One of the main ideas behind Somanet is to eliminate the control cabinets for the robot controller as far as possible through decentralization. There are different standard options for each of the modules mentioned, as well as the possibility of implementing application-specific solutions. The new Safe Motion Module (SMM) is an optional fourth component that is installed between the core and drive. This enables the safety module to monitor, generate and receive safety-critical signals without being dependent on the software in the servo drive.

Safety in the drive controller

The Safe Motion Module is designed for SIL3 (Safety Integrity Level) via FSoE (Fail Safe over Ethercat). The supported safety modes include safely limited speed (SLS) and position (SLP) as well as safely limited torque (SLT). The integration of such safe motion control functions directly into the drive controller offers several advantages:

• A safety PLC (programmable logic controller) can be omitted for most applications. The complete safety handling is shifted to the individual drives.
• Less cabling is required throughout the entire robot arm - for example between redundant encoders and a safety PLC - which reduces costs, complexity and susceptibility to faults.
• Faster signal processing due to shorter paths increases safety.
• Decentralized safety functions - i.e. local 'reflexes' - can be implemented. This means, for example, that a touch-sensitive surface (robot skin) can be connected directly to the servo controller. This reacts directly to sensor events and switches to the correct safety mode accordingly. Normally, the skin would report to a higher-level instance, which in turn switches and monitors the safety mode.
• Cost savings compared to conventional safety solutions thanks to reduced system complexity. This means that robot manufacturers can dispense with the Safety PLC in many applications. In addition, a safe encoder can be saved if two cost-effective, non-safe encoders can be used instead. The effect is even stronger for torque monitoring: only one non-safe sensor is required here, as the safety-relevant redundant signal comes from the current controller itself.
• Faster 'power cycles', i.e. very fast switching on and off.
• Increased productivity, as machines can be accessed in safe mode without having to switch them off. Conventional safety, on the other hand, usually only switches to emergency stop mode. However, the few solutions that already go into 'Safe Motion' today are very complex and cost-intensive.

The SMM supports two encoders and can therefore also guarantee safe motion modes with non-safe encoders. It also offers analog inputs that can be used for extended safety sensors such as touch-sensitive surfaces. This eliminates the need for additional hardware for the safe data request normally required for such artificial 'skins'.

Finally, it is important to emphasize: While safety functions on robotic drives can be of great benefit; they are not a complete safety solution. Rather, the complete robotic system must always be considered when assessing overall safety.

Author:
Nikolai Ensslen is the founder and CEO of Synapticon.