ServoWire Networks operate at up to 400 megabits per second.

ServoWire is fast … delivering state-of-the-art servo performance with digitally networked drives that is comparable to analog torque mode drives.

IEEE 1394 provides fundamental technology which guarantees real-time network determinism and provides extra bandwidth for communication transfers.

With the drive network operating at 400 megabits per second, there is plenty of bandwidth for the servo update rates required in high performance systems. Bandwidth alone, however, doesn’t define fast. The blending of "isochronous and asynchronous" communications is the feature of IEEE 1394 that most uniquely qualifies it as a multimedia and servo network. A Sercos drive network has a similar dual approach to communications, which they call "cyclical and non-cyclical". This method, without the bandwidth to back it up, doesn’t meet high performance servo application needs.

ServoWire isochronous communications occur at regular intervals, up to 8 kilohertz, allowing the transfer of time critical information every 125 microseconds. This capability meets the needs of even the highest performance servo systems. In addition, the pure horsepower of IEEE 1394 provides the ability to transmit a generous amount of other information such as tightly coupled I/O (PLSs, registration sensors, etc.) which must be coordinated with the servo control in many applications.

Since IEEE 1394 has a defined bandwidth roadmap to much higher data rates, ServoWire will be able to address larger numbers of axes and include even more control elegance in the future.

All motion control and servo drive parameters are software-driven --- eliminating physical settings.

No more digital-to-analog conversions at the controller … and no more analog-to-digital conversions at the servo drive. When most controllers are powered by DSPs, and all the modern servo drives are also DSP-based, it’s obvious that digital communications between them makes sense. But until now, high cost and lack-of-speed have kept most servo installations mired in analog transmission of servo drive commands, and using phase-quadrature position feedback.

Traditional analog drive interface

Digital communications allow all drive parameters in a ServoWire system to be defined in software, not by potentiometers. At startup, setup parameters are delivered automatically by the motion controller --- which reads them from the removable system PC Card. Installing a replacement servo drive in the field has never been this simple.

ServoWire Interface

The digital nature of the ServoWire network also provides greater software control and flexibility than ever before. Information is a major part of this flexibility and covers a wide range of areas, from speed and torque of the motor to detailed diagnostic information. While detailed diagnostic information is often known by servo drives, it is rarely available to be transmitted to the operator, or recorded in an event recorder by the system software. Finally, a digital network for servo drives that provides torque mode performance along with the advantages of digital operation.

ServoWire replaces traditional analog interface, eliminating hundreds of electrical terminations with simple, plug-together cables. All drive parameters in system are defined in software, not by potentiometers.

IEEE 1394 provides technology to guarantee delivery of real-time servo information each loop update.

Isochronous transfers guarantee real-time network determinism. ServoWire implements digital torque mode algorithms using key technology within IEEE 1394 that defines an elegant standard for isochronous data transfers.

Isochronous transfers guarantee real-time information is 'absolutely, positively' delivered at a pre-determined rate. This is especially important for just-in-time delivery of data such as time-critical servo loop updates.

The ServoWire protocol allocates network bandwidth for each servo on the network to guarantee timely transmission of torque commands, position feedback, and high-speed I/O status during each loop update for all drives in a ServoWire network.

Including high-speed I/O in the isochronous data channel guarantees that the ServoWire Axis Module can always drive or respond to high-speed I/O (four programmable limit switches and three sensors per drive) on the next loop update.

Many applications benefit from the precise synchronization of high-speed I/O and motion control. Line-oriented manufacturing systems, many within the packaging and converting industries, frequently demand I/O response far beyond the capabilities of PLCs. An example of this is a rotary knife application on a converting machine, where a knife must cut a web of pre-printed boxes to an accuracy of 15 mils at line rates up to 1,200 feet per minute.

IEEE 1394 provides technology to guarantee delivery of real-time servo information each loop update.

The second type of data transfer supported in 1394, asynchronous communications, provides a mechanism for flexibly managing real-time command and status communications on the network.

Asynchronous transfers provide application flexibility

Upon completion of all isochronous transfers in each loop update, the remaining bandwidth is available for asynchronous transfers. Asynchronous communications can be used to:

• enable or disable the drive
• dynamically adjust tuning parameters
• modify drive setup
• monitor system variables in real-time
• transfer diagnostic messages and reset errors
• and more.

Isochronous transfers guarantee real-time network determinism

Many applications can benefit from the ability to adjust system parameters under software control while the servos are operating. One example is adjusting system inertia while motor loads vary in a winding/unwinding operation. The parameter OP_INERTIA is used by the SMLC (ORMEC variable INERTIA@ in MotionBASIC) to let an application program adjust servo loop variables as the roll diameter changes. Dynamically setting servo loop parameters based on roll diameter and tension ServoWire system architecture "on-the-fly" provides repeatable performance and consistent operation over a wide range of operating conditions.

This approach allows high-performance servo systems to handle the combination of large roll diameter changes and load-to-motor inertia mismatches, that can be as large as 1,000 to 1 in high performance winding applications.

No offline, computer-based set-up required to configure new or replacement servo drives.

ServoWire offers true Plug N Play functionality and simplifies new and replacement drive commissioning ServoWire uses plug-n-play technology to bring ease of use to a new level.

IEEE 1394 implements a 'tree' topology, with repeater hardware in each interface rather than a ring (so there is no need for terminators or a hub). The tree structure, and the fact that 1394 uses automatic ID assignment, eliminates the need to set physical addresses before attaching a new servodrive to the network.

ServoWire uses 'plug-n-play' technology provided by IEEE 1394 to expedite setup and commissioning of devices on the ServoWire network. With a ServoWire system, the ORION controller searches for servo drives on the network at power-up. Servo drive IDs are displayed on the drives’ seven-segment LED, and incorrect or unassigned IDs flash until resolved by pressing a button on the drive to select the correct ID. Drive parameters are then downloaded as defined by the software, and can match a single servo drive to a wide variety of motors.

This approach simplifies replacement of servo drives in the field. New drives are installed 'as received' since off-line, computer-based setup is not required to properly configure the new unit. The installer simply selects the appropriate ID, and the servo drive 'self-configures', reducing spare parts and setup complexity.

The fact that 1394 cables provide power for the ServoWire interface in the drives allows the network to operate, even without power to some of the drives in the network.

Thin serial cable technology included in IEEE 1394 open standard slashes interface costs.

The IEEE 1394 standard defines a state-of-the-art interconnection scheme. ServoWire dramatically reduces the installed cost and hassles of system wiring. A traditional servo system has 20-25 connections per servo axis for proper system operation. ServoWire eliminates hundreds of electrical signal terminations with simple, plug-together cables.

The cable and connector design are part of the IEEE 1394 open standard … and are essential technology to delivering the high-speed serial bus communications. Highly engineered and reliable, the cables and connectors are patterned after those made by Nintendo for their Gameboy units.

IEEE 1394 cable design

Standard 1394 cables contain two power conductors, and two twisted pairs (TPA and TPB) for data signaling. Each signal pair is shielded and the entire cable is shielded. Cable power is specified to be from 8 to 40 VDC at up to 1.5 amps and is used to provide interface power for drives connected to the bus.

Molex shipped the first 1394 cables, connectors and headers for use in products. They played a key role to insure that the entire mechanical and electrical designs would be included in the IEEE 1394 standard to guarantee compliant second-source cables would be available.

ServoWire utilizes plug-n-play technology to bring ease-of-use to a new level.

IEEE 1394 implements a 'tree' topology, with repeater hardware in each interface rather than a ring (so there is no need for terminators or a hub). The tree structure, and the fact that 1394 uses automatic ID assignment, eliminates the need to set physical addresses before attaching a new servo drive to the network.

ServoWire uses 'plug-n-play' technology provided by IEEE 1394 to expedite setup and commissioning of devices on the ServoWire network. With a ServoWire system, the ORION controller searches for servo drives on the network at power-up. Servo drive IDs are displayed on the drives’ seven-segment LED, and incorrect or unassigned IDs flash are resolved by pressing a button on the drive to select the correct ID. Drive parameters are downloaded as defined by the software, and can match a single servo drive to a wide variety of motors.

This approach simplifies replacement of servo drives in the field. New drives are installed 'as received' since off-line, computer-based setup is not required to properly configure the new unit. The installer simply selects the appropriate ID, and the servo drive 'self-configures'--- reducing spare parts and setup complexity.

The fact that 1394 cables provide power for the ServoWire interface in the drives allows the network to operate, even without power to some of the drives in the network.

Lower initial purchase price, lower interface costs and lower total installed cost.

ServoWire = performance, ease of use & low cost.

While IEEE 1394 provides superlative performance and specific features for real-time control, its most significant benefit may be its price tag. The technology has been targeted for a wide variety of consumer electronic products and PCs, and has been driven to provide a low cost solution.

Utilized as a servo drive interface, 1394 delivers both simplicity and low cost with its thin serial interface cables. Consequently, ServoWire drive interface costs are less than the traditional analog interface. Another lure of digitally networked drives is the speed and simplicity of wiring, with the resulting reduction in total installed cost.

In the past few years, servo drive prices have been consistently dropping --- with the industry-wide move to more highly integrated power block technology and compact electronic design. Surface mount technology and powerful digital signal processors (DSPs) have allowed industrial servo drives to provide greater value to customers.

We expect this trend to continue and the market should expect greater installation simplicity and lower installed costs for motion control systems. The advantages of networked servo drive technology is so great that prices for a typical ServoWire system will be reduced more than 25%, compared to the existing ORION solution.

This technology, as well with other open standards allows the reduction of system prices.  Servo drive technology is an area ripe for innovation, with more sophisticated levels of technology and software delivered at significantly reduced complexity and lower cost.

IEEE 1394 is an exciting technology that provides a platform for continuing innovation in digital drives and motion control systems in general. Combined with increasing power in the industrial PC and the emergence of Ethernet and TCP/IP as the basis of factory networking connectivity, IEEE 1394 provides a bright future and a basis for continuing, cost-effective improvements in manufacturing productivity.

IEEE 1394b improves on the robustness of IEEE 1394a

IEEE 1394b is the third generation in the evolution of this IEEE standard. IEEE 1394b uses all-digital signalling to improve noise immunity which is critical in industrial environments. IEEE 1394b supports a self healing ring topology, providing a backup data path if a cable connection is severed. IEEE 1394b supports additional media, including Category 5e twisted pair copper, plastic and glass optical cables. Using these alternate media, maximum hop lengths up to 100m are supported.

Compatibility to earlier 1394 versions is maintained, and by using bilingual cables, SMLCs can be connected to older SAC-SM and SAC-SW Servo Drives based on IEEE 1394a.

All current SMLC controllers and SAC-SD Servo Drives use IEEE 1394b. The latest versions of SMLC and SAC-SD Servo Drives also support lock (screw-type) connectors, allowing the cables to be securely fastened to both controller and servo drive.