(SErial Real-time COmmunication System)
is an optical networking standard for motion controllers and drives.
It confers a number of advantages over electrically based, analog
forms of control. Most notably, its fiber optic mode of communication
reduces noise problems seen in electrical systems, while offering
very high signal throughput. SERCOS devices are serially connected
(i.e., "daisy-chained") in a ring
configuration via "nodes,"
each node having its own dedicated receiving and transmitting
ports. Data is sent in "telegrams,"
which contain either control or status information. These are
sent by the controller (master) then received, processed, and
relayed by each node (slave) in the ring.
configured XMP-SERCOS systems connect up to eight (8) nodes. An
additional four nodes may be connected for a maximum total of
twelve (12) nodes. This lends tremendous flexibility to SERCOS-based
motion control systems. In the network example above, a single
ring is featured with three separate drives, each having its own
dedicated node. Almost any combination of nodes and drives is
possible; however, the final configuration and number of drives
within the system is limited by the required cycle time of each
node and the controller. To determine the optimal SERCOS configuration
for your motion control application, please contact
parsing control data and sending feedback, each drive's on-board
processor offers additional capabilities. Depending on the manufacturer,
SERCOS drives have the ability to close a position, velocity,
and/or torque loop, execute internal homing procedures, as well
as latch position based on digital inputs.
the fact that the XMP-SERCOS controller has a different physical
interface than the standard XMP controller, the same MPI is used
for both controllers. The complexity of the XMP-SERCOS controller's
interface has been hidden by the MPI and by the firmware running
on the XMP. The same development tools can be used for both controllers.
The XMP-SERCOS controller requires an initialization procedure
before telegrams can be sent to amplifiers. Once the initialization
procedure has successfully executed, XMP-SERCOS controllers act
the same as standard, analog XMP controllers.
its many advantages, SERCOS does not confer "something
for nothing." XMP-SERCOS controllers share some of the
same limitations as analog controllers:
controllers cannot obtain more from a drive than it's designed
to deliver. When selecting a SERCOS drive, the designer must
scale their selection to the hardware-software requirements
of the system. Different drive systems feature different capabilities
and processing speeds. SERCOS errors arise when a drive is
commanded to do something it cannot do.
most SERCOS drives share a number of standardized user identification
numbers (IDNs), most drive manufacturers assign their own
unique IDNs. If you change drives, IDNs can be expected to
selection of cable length and material (acrylic vs. glass),
transceiver wavelength and power, connector types, etc. all
bear upon the success of a SERCOS network. Hardware flaws
at any point in the SERCOS ring will affect the performance
of the entire system.
upon your choice of motion drives to be used with the XMP-SERCOS
controller, you should consider some or all of the below parameters:
wavelength and power
Engineering's XMP-SERCOS controller uses Agilent Technologies
HFBR-1505A/2505A transceivers for transmitting and receiving
Transceivers used on industry SERCOS drives may differ, depending
upon the manufacturer.
XMP-SERCOS controller transmitter , (HFBR-1505)
incorporates an LED, transmitting at a nominal wavelength
of 650 nm (± 10 nm). Optical peak output power (Pt)
is software adjustable from -18.0 to -5.5 dBm. NOTE: power
is affected by temperature: higher transmitter temperatures
yield slightly decreased power.
Agilent HFBR-2505A receiver's
peak input power varies from -20 dBm (Level Logic HIGH) to
-42 dBm (Level Logic LOW). Data corruption may result if the
receiver is overdriven (inputted optical power too high),
or underdriven (inputted optical power too low). These conditions
are discussed in the next section.
Rate, Cycle Times and Configuring SERCOS
number of devices capable of being operated by one XMP-SERCOS
controller will depend upon the number and cycle times of drives
and the number of networked nodes. It may prove advantageous
to consolidate two or more drives into a lesser or greater number
of nodes, depending upon the task(s) to be accomplished. To
receive guidance on optimizing your SERCOS network, please contact