Achieving safe motion control

SICK Pty Ltd

Wednesday, 04 May, 2016

Achieving safe motion control

In today’s industrial environments, machine and plant operators are faced with a challenging task: creating flexible production workflows with a high level of automation while at the same time ensuring that people, machines and plants stay protected. The way in which interactions between humans and machines are shaped is set to have a significant effect on performance and productivity in tomorrow’s industrial environments.

Innovative safety technology concepts designed by SICK for safe monitoring of drives and machine motions, such as the Safe Motion Control, make it possible to monitor the movement of a machine at any time, helping ensure that interaction between machines and their operators remains safe. By safely monitoring the machine parameters of speed, travel and acceleration, it is possible to draw an exact distinction between the machine movements which are dangerous and those which are safe. According to SICK, this also makes it possible to increase the availability and efficiency of machines while offering a high degree of safety.

All the signals from the safety sensors and actuators can be combined, generating information that indicates whether a machine operator is actually in danger when he or she enters or creates an interruption in a hazardous area. This means that it may be possible for operators to intervene in the machine even while the process is running — preventing interruptions, minimising downtimes and unintended shutdowns, cutting down cycle times, and boosting efficiency and availability in machines and plants.

Safe motion monitoring — external and integrated safety concepts

Safe drive and motion monitoring is based on the safety or control concept being used. Advantages of an external safety concept include:

  • good protection against manipulation due to separation of safety and automation tools;
  • independence from the drive system;
  • entire safety solution in one piece of software;
  • monitoring of multiple drives in a single system;
  • verified and industry-specific application packages, cutting down on engineering work.

According to SICK, drives and axes that are integrated into safety functions should be equipped with certified safety encoders such as the DFS60S Pro. The requirements presented by mobile and stationary applications, and the complexity inherent in safety technology evaluations, indicate that using this kind of technology brings many benefits.

Other motion control sensors

If motors with HIPERFACE technology are being used, the safe Drive Monitor FX3-MOC0 module uses the signal from a HIPERFACE drive for electrically driven axes (eg, in the case of SRS/SRM50, EFS/EFM50 and SKS/SKM36 safe motor feedback systems). This ensures that the necessary shutdown functions are provided and that the required performance level (PL r) is achieved — with a second independent signal (eg, from an encoder) also involved if necessary.

Motion control safety controllers

Flexi Soft and the Drive Monitor FX3-MOC0 can be used to monitor both electrically and hydraulically driven machines. In the event of an interruption of the safety light curtain, for instance, this equipment prevents the need to switch the entire drive control system to a safe energy-free state in order to trigger the required stop response. Drive technology in machine tools — particularly presses — is seeing a shift in favour of electric drives, generally of the servo variety. Electric drives make it possible to feed energy into more specific points in a process, enabling more accurate control of processes, cost savings and improved product quality. The faster traversing movements of the axes also boosts productivity.

Two encoders can be connected to each Drive Monitor FX3-MOC0 module, with the following achievable PLs:
  • PL e for one axis with non-safe motor feedback (MFB) and additional external encoder.
  • Up to PL d for two axes, depending on the motor feedback being used (safe or non-safe MFB) and without an additional external encoder.
  • PL d for one axis and a DFS60S Pro safety encoder.

Safe monitoring of automated guided vehicles

The SICK Safe Motion Control solution, consisting of the DFS60S Pro safety encoder and the Drive Monitor FX3-MOC0, is a suitable solution when it comes to safe drive and motion monitoring for mobile machinery such as automated guided vehicles (AGVs). This solution helps machine manufacturers and system integrators save time during not only system engineering, but approval procedures too. What is more, it keeps technical and legal risks to a minimum, such as those associated with self-evaluation of solutions using non-safety-certified standard products. The Drive Monitor FX3-MOC0 expansion module developed for the Flexi Soft safety controller reliably captures the direction of travel and speed parameters of the AGV, as well as providing all the most commonly used interfaces for encoders. Encoders can be connected to the Drive Monitor FX3-MOC0 at a central point and used for monitoring the direction of travel, the speed or even the brake ramp. This monitoring feature opens up the possibility of optimising the protective fields associated with the safety laser scanner attached to the AGV — and the space available for movements to take place can be used more efficiently as a result.

DFS60S Pro safety encoder — safe monitoring with just one encoder

The DFS60S Pro safety encoder is attached to the AGV’s drive axis and provides support for performing safety functions such as SSM (safe speed monitor) and SLS (safely-limited speed). Interaction between the encoder and the control system enables the control system to reduce the speed of the AGV as necessary. The SBC (safe brake control) and SS1 (safe stop 1) or SS2 (safe stop 2) drive monitoring functions make it possible to trigger and safely monitor an emergency stop of the AGV. This encoder also acts as a signalling device for AGVs that have complex navigation requirements. As these vehicles are given more freedom to move around, safe movement monitoring has to overcome the obstacles that this brings.

Transport vehicles with differential drives feature two independent drive units, enabling movements such as rotation on the spot. Without safety-certified encoders, executing complex processes like these would require significant time and effort to be spent on creating the right control system. The certified DFS60S Pro, on the other hand, provides a simple and safe way of recording direction of travel and speed information. In turn, this makes it possible to create separate, independent travel profiles for vehicles.

Advantages of an integrated safety concept

This concept can be implemented using not only HIPERFACE motor feedback systems (SRS/SRM50 and SKS/SMK36), but also motor feedback systems featuring the HIPERFACE DSL digital interface (EFS/EFM50 and EKS/EKM36). The single-cable technology used with HIPERFACE DSL cuts the amount of cabling work the manufacturer has to do in half.  Advantages include:

  • Only a few male connectors and cables are required.
  • Fewer components.
  • Complete drive system from one manufacturer.
  • Quick certification.
  • Short response time for errors.
  • Easy availability of the control parameters.
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