Friday 8 June 2012

Precision motion control

A range of servo drives for precision motion control that can boost performance and slash system building costs in dozens of common industrial automation applications has been launched by Metronix. The new drives offer a peak current capability that is up to twice that of many similar drives on the market, allowing machine builders to dramatically boost acceleration times.

An increased overcurrent capability of four times the continuous output rating is being offered as standard on Metronix' ARS 2000 FS range of Ethernet-compatible servo drives. This compares with the ~2 to 2.5 times overcurrent rating offered by many other servo drive manufacturers.

The capability can be exploited in many common motion control applications to increase the speed of moves and the overall throughput of machines. In tests that compared drives offering a two times overcurrent capability against the new ARS 2000 FS, using a range of loads on rotary and linear servo motor axes, the new drives shortened travel times by factors from around 17 to 25 %. The drives will sustain the overcurrent for half a second, providing considerable flexibility for the system builder.

Depending on the application and the motion profiles used, faster acceleration can have a significant impact on machine cycle times. Point-to-point moves are the most frequently used type of motion on many machines for example. Here, Metronix' ARS 2000 FS can dramatically shorten the times required to accelerate up to full speed when using common motion profiles such as trapezoids or S-curves.

This kind of movement features extensively in many automation applications such as pick and place, parts handling and assembly, labelling and packaging, and sampling and testing. In continuous applications such as these, Metronix' tests demonstrated overall increases in automation productivity of around 5 to 7% by switching to the new drives.

The faster acceleration results from an uprated IGBT power stage, which utilizes power factor correction to boost the internal DC bus voltage level and allow the motor to reach higher top speeds. This adds only a fractional cost to the drive.

Metronix developed the capability to provide a closer match between drive and servo motor capabilities. Many servo motors offer an overcurrent capability that is higher than the typical drive's overcurrent ratio of around two. Ratios from three to four are common, and they can be even higher. By using Metronix drives, machine builders are able to exploit the full continuous and peak torque capabilities of the servo motor. In some applications, it's also anticipated that users will also be able to select a smaller servo drive, cutting a substantial amount from the bill-of-materials - as the drives are usually the most expensive part of the motion control system.

"This capability provides automation builders with a means of reducing machine cycle times for faster payback, and potentially reducing bill-of-materials costs as well," says Metronix' Product Manager, Frank Essmann. "Some simple calculations at the start of a machine design project are all that's needed to evaluate the potential improvements that can be gained."

ARS 2000 FS is a family of compact panel/cabinet-mounting drives available with a choice of six single- or three-phase continuous output power ratings from 0.5 to 6 kVA, in two case sizes with widths of 59 or 69 mm (2.32 or 2.72 inches). The drives all feature a universal encoder interfacing capability that allows connection to resolvers, analog/digital incremental encoders, and single/multiturn absolute encoders such as Hiperface or EnDat. Standard communications interfaces include Ethernet, USB and the CAN fieldbus - compatible with the DS 402 CANopen device profile. The drives also come with a built-in EMC filter, integrated brake chopper and brake resistor. Two expansion bus slots accepting plug-in modules provide a very powerful means of extending a drive's capability for specific applications. Among the options available are a motion control module that can control up to four interpolated axes, digital I/O, additional networking interfaces including EtherCAT or Profibus-DP, and a functional safety module compliant with EN 61800-5-2.

The motion control plug-in adds another powerful mechanism to the cost-saving potential of Metronix' new drives, providing the means to convert an ARS 2000 FS into a very economic intelligent drive. As the module can also control up to four interpolated axes, it can greatly reduce the costs of many common assembly, manufacturing and processing motion control applications such as product synchronization or spacing, registration, labelling, cutting, pick-and-place, and wrapping. Complex applications involving three axes of control, plus a feed or handling axis, can even be accommodated using the economic plug-in module. A powerful Windows-based programming and configuration software tool is available to users to create embedded motion and machine control software for Metronix systems.

Metronix has been producing motion control technology for industrial machines and automotive applications for over 30 years. Its product range includes smart servo drives with integrated positioning capability, plus motion controllers and accessories that provide cost-effective solutions for multi-axis motion control and automation, and decentralized machine control requirements. A key feature of Metronix' motion products is their rich networking and encoder interfacing capability, which ensures that drives can be integrated easily into virtually any industrial system or machine - even if an OEM has custom PLC or control hardware. This feature is highly valued by many OEMs as it allows them to create and continue developing innovative brands of machine offering unique features. Metronix complements this capability with what is probably the most sophisticated and capable custom drive engineering service on the market today. Motion control products designed by Metronix are marketed under its own brand, and in custom forms by a number of well known industrial OEMs.

The company additionally makes geophysical instruments and customer-specific digital controls for measurement and control applications. Metronix is part of the Apex Tool Group, headquartered in Sparks, Maryland, USA. The Apex Tool Group has more than 7,600 employees in over 30 countries. Metronix' design and manufacturing facility is located in Braunschweig, Germany.

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