SERCOS III offers several advantages:

• Compatible with previous SERCOS interface (topology, profiles, telegram structures, synchronization)
• Reduces per-node interface costs by offering powerful, lowpriced hardware, including FPGAs and multiprotocol controllers
• Integrates IP protocols
• Enables cross-communication between slaves
• Synchronizes several motion controls
• Tolerates faults with a double-ring signal flow structure in case of a break in the ring
• Allows hot plugging for connecting and removing nodes during operation
• Provides safety protocol for drive-integrated safety functions
• Can operate at half the previous SERCOS minimum cycle time (from 62.5 to 31.25 µs)

Topology

Like the original SERCOS, SERCOS III has a ring structure. The difference is that SERCOS III employs a single daisychained Ethernet cable, which has a double-ring structure regarding signal flow for redundant data transfer. Therefore, if the ring breaks at any point, communication and manufacturing can continue, while an integrated diagnostics tool signals the break to an HMI.

Besides the double-ring, a line structure (single ring) is also possible in SERCOS III. While this doesn't offer redundancy, it does save a wire connection.

Centralized and decentralized drive concepts

SERCOS III halves the minimum cycle time of SERCOS from 62.5 to 31.25 µs, due to industrial Ethernet's high bandwidth. Up to 254 devices can be connected on a ring, and numerous rings can be implemented. As a result, SERCOS III supports both centralized signal processing and decentralized drive concepts. With centralized concepts, the drive closes only the current loop, whereas all other axes' loops are implemented in the central control electronics. In a decentralized configuration, the drive closes all control loops.

Synchronizing motion controls

SERCOS III specifies a profile for distributed control in modular machines and systems, allowing controller-to-controller synchronization between motion controls. This allows individual machine modules to be integrated into communication networks in real time without writing special software. The SERCOS C2C (Controller-to-Controller synchronization and communication) profile standardizes this type of communication and supplements existing SERCOS device profiles for servo drives and remote I/O devices. Typical profile applications are in printing, packaging, and processing machines, and machine tools that require special control systems and synchronization, such as gantry axes or rotary transfer tables.

Chips give options

Compared to SERCOS I and II, which utilize ASICs, SERCOS III employs standard modules such as FPGAs or General Purpose Communication Controllers (GPCC), thus reducing costs per node. To further decrease prices, industrial Ethernet connectors and copper-wire cables are used in place of fiber-optic cables and couplings; however, fiber optics will be available in SERCOS III for special applications.

FPGA controllers

A software core (SERCOS III IP) lets system manufacturers combine SERCOS III hardware and their logic components in one common FPGA, which includes all hardware functions such as timing, synchronization, and processing of cyclic and noncyclic data built on two integrated Ethernet MACs. FPGAs from Xilinx and Altera are supported.

GPCC controllers

The SERCOS core has been integrated into a General Purpose Communication Controller (GPCC) — the Hilscher netX 500 — an ARM9260-based System-on-Chip network controller. NetX enables end users to implement control and drive devices that can be adjusted to one of several available industrial Ethernet protocols through appropriate driver software. This benefits OEMs as they will handle just one type of wiring and end users who won't need various hardware configurations for each industrial Ethernet protocol in a plant.

Drive performance on a single ring
Data size (bytes)	Cycle time	Number of drives	Type of cyclic data
8	31.25 µs	8	Torque command, actual position
12	250 µs	70	Speed command and actual value, position command and actual value
16	1 ms	254	Numerous command and actual values for the maximum number of drives in a ring.
32	1 ms	150	Numerous command and actual values
SERCOS uses hardware synchronization with a submicrosecond jitter for precise, real time control. SERCOS III increases transmission speed over SERCOS I and II. Here are some typical values.

SERCOS III vs. I and II
	CYCLE TIMES	SYNCHRONIZATION	APPLICATION AREAS
Standard industrial Ethernet	Not cyclic	Not synchronized	SERCOS III if the IP channel is used without the cyclic real-time channel
Positioning drives, FCs, I/Os	4 to 10 msec	>4 msec	SERCOS III
Controller-to-controller communication and synchronization	1 to 10 msec	<1 to 10 µsec	SERCOS III
Coordinated drives, high-speed I/Os	250 µsec to 4 msec	<1 µsec	SERCOS I, II, and III
Multiaxis drive concepts with centralized signal processing	31.25 µsec to 125 µsec	<1 µsec	SERCOS I, II, and III
Over the years, the automation industry has relied on five real-time communication types. The SERCOS generations answer each area.

 

For more information on SERCOS III, please visit www.sercos.com