SCALABLE FUNCTIONAL SAFETY ARCHITECTURE ADDRESSES NEEDS OF SPECIALIST CNC MACHINE BUILDERS

Complies with EN 13849-1 up to PL e, and EN 61800-5-2 up to SIL 3 -----Minimizes need for additional safety-related hardware and wiring

Naperville, IL, January 28, 2013 --- NUM has released a sophisticated

system-wide functional safety architecture for its CNC system, providing an
exceptionally scalable solution that can be applied very easily to almost
any type of machine tool - regardless of complexity or number of axes. Known
as NUMSafe, it includes a dedicated safety PLC, safe input and output
modules, and digital servo drives with built-in safe motion monitoring. It
is compatible with NUM's new-generation Flexium+ CNC platform.

According to NUM's Chief Technical Officer, Massimiliano Menegotto,
"Functional safety is becoming a mandatory requirement for most types of
machine tool, independent of the machine's performance, accuracy and
complexity. As well as improving operator safety, it also increases machine
productivity and availability. NUMSafe's inherent scalability and
versatility of control gives OEMs a simple solution, regardless of whether
the end product is a basic 3-axis machine, or some highly complex machine
with a hundred-plus axes for an application such as rotary transfer
machining."

Until relatively recently, designers wishing to implement even basic
functional safety schemes on CNC machines were forced to use
electromechanical safety technology such as special contactors and relays.
This approach involved significant extra component and wiring costs, as well
as increased machine development and build times. By integrating safety
functionality across the entire CNC platform NUMSafe minimizes the need for
additional hardware and simplifies software development, to OEM's
considerable advantage. Furthermore, end users benefit from a strong
increase in machine productivity because it is no longer necessary to power
off the complete machine every time there is an element of human
interaction; instead, protection can be ensured by dedicated functions which
limit the movement, speed and position of axes.

A key advantage of the NUMSafe architecture is that safe devices such as the
safety PLC and I/O modules can be contained within the same standard
terminal line up as other elements of the control system. All communication
between the machine's control system, operator panel and servo drives is
handled via EtherCAT field bus, using a Fail Safe over EtherCAT (FSoE)
protocol to ensure integrity of safety-related data. NUMSafe complies with
the EN ISO 13849-1 machinery safety standard up to PL e, and with the EN
61800-5-2 functional safety standard for variable speed drives, up to SIL 3.

To help machine builders minimize development time the application programs
for the safety PLC are created using the same suite of powerful software
tools that is used to commission the entire system, including the CNC, PLC,
drives and I/O modules. The logic of the safety application is programmed
using function blocks such as 'E-Stop', 'Operation Mode', 'AND', 'OR, etc,
linked to safe inputs and outputs.

Complex safety functions can be set up easily by chaining function blocks.
For example, requesting the machine operator to perform an action requiring
use of both hands - such as operating two control switches simultaneously -
to prevent exposure to moving parts, and verifying this before allowing
execution of any motion command, only requires a couple of instructions. The
safety application is a self-contained program; as soon as the developer is
satisfied with its logic it can be downloaded to the safety PLC.

NUM's latest NUMDrive X digital servo drives, which are available in mono-
and bi-axes versions, can incorporate a safe motion monitoring module that
operates in conjunction with the safety PLC to oversee and control all
safety-related aspects of drive and motor behavior. By allowing safety
functions to be implemented on individual machine axes, and only where
required, this modular approach helps reduce system cost. Furthermore, NUM
offers two versions of the module, enabling designers to match their
application needs very precisely. Both versions feature redundant channel
architecture and use cross-monitoring techniques to ensure data integrity.

The basic safe motion monitoring module provides a Safe Torque Off (STO)
function; this is the most commonly used safety function and ensures that
the drive can longer command the motor to generate torque, with continuous
monitoring to prevent unexpected start-up. In addition to STO, the extended
version of the module implements the EN 61800-5-2 compliant functions of
Safe Operating Stop (SOS), Safe Stop 1 (SS1), Safe Stop 2 (SS2),
Safely-Limited Speed (SLS) and Safely-Limited Position (SLP) either by means
of safe homing and incremental encoders, or by employing certified absolute
encoders such as those used with NUM's new line of innovative single-cable
servo motors.

Used singly or in combination, these functions enable designers to implement
a wide range of machine safety concepts. For example, SS2 safely monitors
that the braking of an axis is as quick as possible in the event of an
emergency. This can be followed by the SOS function to instruct the
drive/motor to maintain a fixed position by generating a degree of holding
torque, but not to move - the axis is monitored continuously to ensure that
it remains stationary.

Another cost-saving benefit of NUM's safety architecture is that there is no
need for an additional encoder on machine axes that implement safety
functions. Motor feedback can be derived from safe encoders which return
position and redundant position data to the drive using a secure certified
protocol, or, in the case of synchronous motors, any standard sin/cos
encoder.

NUM's extensive portfolio of motors includes two ranges of brushless
servomotors which only require a single cable interconnection. Developed
specifically for use with NUMDrive X servo drives, these employ an
innovative safe digital encoder interface scheme which carries encoder power
and position feedback data (redundantly) on a two-wire link embedded within
the motor's power cable. As well as reducing cabling costs, this approach
further improves machine safety and reliability by reducing the number of
interconnections that are needed.

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