Machine Controllers: Smarter and Faster
With faster, improved CNC equipment, manufacturers keep metalcutting under control
By Patrick Waurzyniak
Machine control hardware continues to rapidly evolve with the latest CNCs featuring faster processors, increased memory, solid-state flash storage, plus improved servos and bus architectures. With higher throughput capacity, the new controls promise efficiency and productivity gains for manufacturers seeking to wring the absolute maximum performance from their machine tool equipment.
In this tightly contested field, control suppliers' highest-end CNC controls may offer manufacturers the most bang for the buck, but recent introductions also include lower-cost models to help broaden controls vendors range of equipment. Worldwide controls leaders Siemens AG (Germany) and GE Fanuc Automation Americas Inc. (Charlottesville, VA) lead the pack, but renewed competition from smaller players including Bosch Rexroth Corp. (Hoffman Estates, IL), Heidenhain Corp. (Schaumburg, IL), and Fagor Automation (Millersport, OH), also offer machine tool buyers alternatives.
Among the hardware advances, Siemens' latest version of its Sinumerik 840D control includes a new numerical control unit, the NCU 573.5, announced at WESTEC. When used with the integrated PLC 317-2DP, the new NCU is said to provide users with approximately 160% higher NC performance and 300% more PLC performance over previous versions, as well as greatly expanded CNC memory. When expanded to the maximum memory, the NCU 573.5 controls 31 axes/spindles and 10 channels/10 mode groups.
The new NCU is an evolution of Siemens' advances in NCUs for the Sinumerik 840D control, notes Michael Sutherland, applications engineer, Siemens Machine Tool Business Unit (Elk Grove Village, IL). "In a large way, it's following the basic PC technology, to some extent, with faster processors, which allows better block cycle times in our control," Sutherland says. "We upgraded the PLC CPU to a faster version, with memory capacity, and we increased the available memory to the end user."
The new system offers up to 6 MB of memory, with 3 MB memory as standard, and the PLC CPU has been upgraded to a Pentium III processor. "Essentially, the faster processor allows us to increase our block cycle time, which in turn speeds up the system," Sutherland adds. "It's particularly noticeable in high-end mold-and-die-type applications, whether it be three-axis or five-axis machining, where you are going to be see better performance from the machine. We see an increase in the actual performance when we get it into a real application, and certainly mold-and-die and aerospace users are always looking for increases in performance."
With the latest 840D control, users with very complex machines also can manipulate more than the maximum 31 axes controlled by one NCU by employing multiple NCUs. "Each of our NCUs can control 31 axes, so if you need to go beyond that we can slave 16 NCUs together," Sutherland says. "We do have some cases of machines running 40 and 50 axes, and often then we may even just dedicate one NCU to controlling the process, and let other NCUs handle the axes."
Faster servos, processors, and an improved bus architecture power GE Fanuc Automation's completely redesigned 30i family of CNCs, which can control up to 32 servo axes and eight spindle axes. In the new CNCs, a highly integrated system using new PowerPC RISC processors provides more punch for managing manufacturing tasks, while a new bus architecture and improved servo systems also help improve machine throughput.
"To improve reliability, we've done things like adding ECC [error-correction-code] bus-checking hardware," says Bill Griffith, GE Fanuc Automation CNC product manager. "It's part of the RAM, and while our servo systems have had it for some time, the 30 series is the first CNC to have ECC."
The improved bus architecture enables the GE Fanuc control to drive 10 paths, allowing simultaneous execution of 10 different CNC part programs. "We've made significant changes to the bus, all to accommodate our software features that enable things like block processing time that now is down to 400 µsec," notes Griffith. "The control will automatically adjust the feed rates to provide the highest possible feed rate for the operation."
The new 30i family uses the same instruction set as the PowerPC RISC family, with the processors from IBM requiring less power and generating less heat, he adds. "We've also redesigned the operator station and added both vertical and horizontal soft keys, plus we have new software that reduces setup time with the Manual Guide i software, which means you don't have to know anything about programming," Griffith says. "As we continue to evolve our CNC, we're continuing to look for ways to drive lean, reduce setup times, and improve productivity.
"Another thing we've done is redesign the PMC, the programmable machine control, that's like our PLC, and that's where the machine tool builders add software. This PMC is also a lot faster, which will result in decreased ancillary time on the machine, less time for a tool change. The PMC has very fast execution, has 25 nsec per step, and we've also increased our scanning I/O rate."
Larger flash memory on GE Fanuc's new controls also allows for improved data backup with an automatic system backup performed every time the CNC powers up, Griffith says. "We've provided a lot of features so that when our system does go down, you can recover from it more quickly, and this is a hardware improvement." The system's larger built-in flash ROM enables operators to simply push a restore button in case of a shutdown.
Improved servos enable enhancements to GE Fanuc controls' precision, adds Griffith. "In the CNC, we've done a lot to improve precision and provide very smooth motor control with nanometer interpolation," he says. "Our nanosmoothing interpolation allows users to achieve the same results as a NURBS CAM processor without having that NURBS processor, and the only reason we can do this is because of the changes in the servo system."
With GE Fanuc's improved servos, the servo axis control card and amplifiers are more tightly integrated with the CNC, making for very tight loops, according to Paul Webster, GE Fanuc servo product manager. The systems feature new DSPs, the TI 54 series, and the faster Fanuc Servo Serial Bus (FSSB), which previously ran at 50 MHz, now runs at 131 MHz, allowing users to close the loop faster and perform quicker, Webster says. "As our DSPs and processors get faster, we can update our loops faster," he adds.
Another servo enhancement is the servos now are capable of 16 million pulses per rotation, so the interpolation is much better, Webster notes, with 10 times more accuracy. GE Fanuc also has added more rare-earth magnet motors to the core design, and at WESTEC the company showed its new low-cost Beta HVIS series servomotors that use a rare earth, high-density permanent magnet.
High-speed milling can be performed with the open-architecture Bosch Rexroth IndraMotion MTX control. (Inset:) The IndraMotion system features CNC kernel capable of being customized by machine builders and an improved servodrive system.
Open control architecture used with Bosch Rexroth's latest control, the Rexroth IndraMotion MTX, makes the system an easily customizeable unit for machine tool builders interested in tailoring the new control's CNC kernel to meet their specific needs, according to Rick Rey, IndraDrive and IndraControl product manager for Bosch Rexroth Electric Drives & Controls (Hoffman Estates, IL).
Introduced at IMTS, the IndraMotion MTX control succeeds Bosch Rexroth's previous control, the MTC 200, and adds several new enhancements to both hardware and software capabilities. "It's a new architecture, and the first release is going to be a PC card inside of an HMI unit," Rey says. "The PC card incorporates the interface for SERCOS for motion, and there's also a Profibus interface for remote I/O. All our operation panels, machine operator panels, will also be operated under Profibus.
The IndraMotion MTX supports Profibus, Interbus, and integrated multitasking of the PLC with the IEC 61131-3 standard. A new PLC functions under the VXWorks real-time operating system. "The IndraWorks platform is the basis of our PLC in our new product line, and IndraWorks will be used across all of the Rexroth control systems, whether it be a PC control, a hardware-based control such as the MTX, or our servodrive control.
"What's also new in the IndraDrive is the option to have an integrated PLC in the drive," Rey adds. "With that function, users can have single-axis applications in the drive that don't require a hierarchy control system. The drive can run on its own with the logic, and we use motion function blocks that are based on PLC Open Definition."
Among the new hardware for the MTX controller, the control features the IndraControl V HMI with a new panel, IndraControl VDP, plus the IndraControl IPC 40 industrial computer. Servodrive improvements include a scaleable IndraDrive system with up to 120-kW power. "The IndraDrive is modular, so it has a power section and a control section. The control section can be configured to each application, so the IndraDrive can run as a VFD, or Variable Frequency Drive, it could run as a Closed Loop Servodrive, and it can run as a main spindle drive," Rey says. "So you're basically minimizing the type of hardware used, and we're changing what type of control section in the drive is needed for the type of function."
The Rexroth drives work SERCOS, Rey adds. "The IndraMotion MTX is only SERCOS. All Rexroth controls are SERCOS-based; however, the drives can run SERCOS, analog, and Profibus, and we will also be coming out with a DeviceNet interface later this year."
An updated power supply from Heidenhain Corp. (Schaumburg, IL) offers users a lower-cost method of upgrading analog machines with the latest iTNC 530 contouring control. Introduced at WESTEC, the new UV 106 power supply enables meeting the needs of CNC machine retrofit applications where users want to upgrade their existing drives or a simple analog system for use with the iTNC 530 control. The new configuration makes Heidenhain's top control available to more users, and also reduces the cost of the control system considerably.
"It's meant for retrofit applications, where a guy has existing analog drives and motors that are still fine, but he wants to upgrade his control technology," says Chris Weber, Heidenhain product manager. "We've introduced a more cost-effective method for upgrading analog machine components for use with the iTNC 530. It allows you to use a much less expensive interface to an analog drive system.
The new UV 106 power supply can be used to form the basis for a cost-effective analog control system by negating the requirement for the Heidenhain CC 422 controller unit as the on-board DSPs are not used with an analog system. When combined with the Heidenhain MC 420 main computer, a four- or five-axis system can be achieved for simpler machines. According to Heidenhain, with the MC 422B anywhere from four to 10 axes can be controlled on more complex machines where five-axis simultaneous contouring or high-speed machining functionality is needed.
"We've always had the ability to interface to analog drives but you had to buy a component that you didn't use," Weber adds. "Basically you had a lot of DSPs built into what was the computer controller, and you needed that to actually interface the analog drive system. We've removed the requirement for that entire component."
Demanding machining applications can utilize the Fagor Automation 8055 and 8070 CNCs, according to Todd Drane of Fagor Automation Corp. (Millersport, OH, and Mondragón, Spain). The 8070 control now has the ability personalize up to six different kinematics for five-axis machining, Drane notes, and the CNC can control spherical, orthogonal, and angled spindles as well as tilting rotary tables.
"We have reduced block processing time down to one-half a millisecond, thus 2000 blocks per second can be executed," Drane states. "Due to the extremely fast block-processing speed, block look-ahead has also been increased to 300 blocks, which improves cycle time and part finish.
"The CNC 8070 utilizes Jerk Control, which automatically applies the appropriate amount of acceleration control that creates smooth path transitions and consequently less mechanical stress on the machine," he says. "But in addition, we now allow the definition of post-interpolation filters which help eliminate all mechanical resonance frequencies. These are essential features for high-speed machining, particularly within the aerospace industry."
Drane also notes that the CNC 8055 and CNC 8070 are equipped with an on-board intelligent profile editor that acts as an on-board CAD/CAM system. "With the profile editor, complex profiles are quickly and easily created and then associated with the appropriate programs for easy profile subroutine calls. Even if the operator/programmer does not have all of the profile data necessary, the intelligent profile editor will automatically calculate alternative profile data points to the operator, thus allowing for the correct choice to be chosen."
The updated Fagor CNCs also feature tool life management, allowing monitoring of the tool cycle time, and either automatic replacement of the tool or automatically modifying the tool wear offsets for each tool based upon the cycle time of each tool.
This article was first published in the June 2005 edition of Manufacturing Engineering magazine.