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Ethernet encoders deliver new levels of monitoring and control

Ethernet encoders deliver new levels of monitoring and control Absolute encoders are the unsung workhorses of factory operations, essential to the fine control of automated and rotating axis machinery. Now, product innovations from SICK have delivered design and connectivity improvements which promise to improve production control and plant availability through unprecedented levels of reliability and accuracy, as well as enhanced monitoring and diagnostics. Darren Pratt, encoder specialst at SICK (UK), explains.

With Industrial Ethernet compatibility, including EtherNet/IP, EtherCAT and PROFINET protocols, new SICK Industrial Ethernet encoders utilise embedded switch technology to enable use in Star, Line or Ring topologies. The EtherNet/IP versions are the first encoders to integrate DLR (Device Level Ring) technology for continuous monitoring of network integrity in a ring topology.

The SICK AFS60 single-turn and the AFM60 multi-turn programmable absolute encoders are rotary sensors for detecting paths, angles, speeds and positions in operating machinery. They are designed to perform equally well in both precision applications and for harsh industrial conditions with enclosure ratings of IP65 or IP67 and with a wide temperature range from -30°C to +85°C. The tough nickel-code disk eliminates the risk of damage during operation, and an increased separation distance between ball-bearings minimises vibrations for smoother operation plus reduced wear and tear.

Both the AFS60 and the AFM60 encoders can be easily programmed and reprogrammed to meet variations in requirements, allowing operators to quickly commission and change parameters. Their application offers advantages to manufacturers and integrators of a broad range of production processes, handling systems, production machines, print systems, measurement and inspection equipment.

Improved communication
Ring topology integration offers many advantages in factory-wide control networks. The benefits include redundancy and protection against communication failure, as well as reduced cabling requirements when compared to star topologies. The EtherNet/IP variants of SICK's AFS60 and AFM60 encoders were the first encoders available on the market equipped with Device Level Ring (DLR) capability to take full advantage of ring topology. This allows them to be integrated in a redundantly constructed ring topology - a first in the encoder world. DLR ensures permanent monitoring of the ring and attached devices.

By conforming to the specifications defined by the Open DeviceNet Vendor Association (ODVA), the integrated DLR functionality of the AFS60/AFM60 is significant because it allows maximum machine availability.

Seamless network reconstruction
If there is a fault in the ring, for example a cable break, devices and applications can be contacted from the other direction so that continued communication via the ring - or the line remaining in existence - is ensured without time loss, maintaining application availability. Furthermore, the controller receives information on where exactly in the ring the fault has occurred, which enables the fault to be quickly located for correction.

Network management via the encoder is enabled through its Embedded Switch Technology, so that there is no need for external switches. The EtherNet/IP encoder can handle and pass on 'check packages', so-called beacon frames, via its dual port switch to test the ring constantly, taking only a few microseconds. In this way, constant and active availability tests of the network participants and the connections between them can be carried out. In the case of a device fault or broken cable, the participants are contacted from the other side within less than 3 milliseconds.

This change of direction of transmission ensures smooth communication between the devices and the controller if there is a fault. The DLR functionality therefore offers users intelligent redundancy and rapid fault detection which can considerably increase the reliability of the network, and thus the availability of machines and plant.

Full Ethernet connection
In the past motor controllers often featured traditional fieldbus interfaces for networking to PLCs, SCADA systems and connection to auxiliary absolute encoders for axis following applications. Today, more motor controllers are entering the market with Industrial Ethernet interfaces in place of the traditional fieldbus interfaces to enable faster, more deterministic data transfer.   

PLC manufacturers are also offering their Industrial Ethernet-based fieldbus interfaces at relatively attractive prices. As a result, many machine builders are already converting existing machine generations to Ethernet-based fieldbus systems, as well as expecting improved performance by changing to, for example, EtherNet/IP, PROFINET or EtherCAT.

From the control system producers' viewpoint, IT integration and commissioning needs to be simple. For their customers, increased plant availability and improved diagnostic functions for early detection of any problems are particularly important. To ensure optimum benefit from this improved communication between devices and applications in the control networks, this fieldbus capability must be matched by absolute encoder design and communication functionality. Hence, the importance of the introduction of the Industrial Ethernet AFS60/AFM60 encoder families from SICK, which offer full compatibility with these Ethernet protocols.

Improved machine availability
The portfolio of SICK Ethernet-based fieldbus encoders includes sensors with connections for EtherNet/IP, PROFINET or EtherCAT protocols. The proven and robust AFS60/AFM60 encoder technology is characterised by the device resolution being independent of the operating speed. This feature enables maximum resolution without limitations, even at maximum rotary speeds, for greater accuracy in accumulating operating data.

All three protocol versions also offer unmatched comprehensive diagnostic possibilities to optimise failsafe performance and increase plant availability. To achieve this capability, the individual potential fault messages are hierarchically structured in the form of so-called flags, alarms and warnings, depending on their importance for the current operating state. Not every message immediately triggers a machine stop, but only those that could immediately lead to a malfunction. The other messages can be prioritised and processed, for example within the framework of preventive maintenance.

Examples of the extensive diagnostic functions of the Ethernet AFS60/AFM60 encoders which help continuously monitor plant condition and prevent unforeseen downtime include:
  • Five dual-colour LEDs on every encoder continuously show the current operating state of encoder functions and data transfer.  
  • Two operating hour counters - one starts when power is switched on while the other monitors shaft rotation.  This information can be utilised to create preventative maintenance alerts relating to the mechanical components connected to the encoder.
  • User-programmable encoder temperature limits, so that when a SICK EtherNet/IP or EtherCAT encoder reaches the defined maximum or minimum value, the encoder generates a message to the controller warning of a potentially critical state.
  • Programmable position limit values can be configured in EtherNet/IP and EtherCAT variants, to create so-called cam functionality or 'soft' limits.
  • Speed detection feedback can be used to protect the process. By monitoring these values, speed-sensitive components in the drive chain can be protected.  Configurable limits can be created in EtherNet/IP and EtherCAT variants.  

Rotary axis function
Each AFM60 multi-turn Ethernet encoder has another feature that reduces the time and costs for machine integration: the rotary axis function which particularly benefits rotary tables and drives using transmission or reduction gears. This innovative 'round loop' technology cuts programming and hardware costs for machine builders by enabling the number of encoded rotations to be defined as a fraction, an important function for rotary applications such as turntables or power presses which often have gearing between the encoder and rotating axis.

For example, if the encoder is connected to a rotary table via a 10:125 gear ratio, the encoder value must change from its maximum value to zero after exactly 125/10 turns to avoid errors. In most other programmable encoders, the total number of turns can only be programmed to a value which can be represented by a value which equates to 2n (ie 32, 64, 128 etc), and not a fraction, thus introducing a cumulative error.  

The rotary axis function of the Ethernet AFM60 enables the number of turns to be perfectly matched with the gear train driving the encoder, saving machine constructors complicated gear PLC calculations and controller programming. The result is smaller PLC programs and cost saving during installation, maintenance and service.

Ethernet encoders from SICK
With their comprehensive diagnostic possibilities, their rotary axis function, and the DLR network management of the EtherNet/IP versions, the AFS60 and the AFM60 Ethernet-based fieldbus encoders from SICK meet customer expectations for economical rotating machinery control solutions. The encoders offer easy installation and commissioning, and ensure maximum failsafe performance and plant availability during operation through the early detection of critical operating states.
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