A new quartet of sophisticated servo drives
01 February 2008
This foursome is headed for the general machinery automation market.
Control Techniques' servo drives
Thanks to servo motors, highly synchronised motion control is becoming more widespread in factory floor equipment such as packaging, pick-and-place or gluing machines, material handling, X-Y tables and profiling machines. Servomotors are well liked these days: they are physically robust, they can be networked and synchronised with great precision, and they have become much easier to program.
Drive manufacturers like Control Techniques have seen this growing ‘general machine market’ opportunity. And it’s different from what the machine tool industry looks for in motion control. Machine tools have a critical need for good velocity control, for operations like contouring where the tool is continuously cutting into metal. Packaging machines, on the other hand, have more discontinuous ‘point to point’ operation, or ‘pulse duty’ as Control Techniques refers to it. Or ‘indexing.’ The start and stop motion—often in brisk, highly repetitive cycles— needs to be precise, but what happens in between the start and the stop isn’t so important. As a consequence the drives need to function more dynamically, with greater torque overloads. A machine tool drive might be built to withstand, for example, 175% overload; Control Techniques’ new Digitax ST drives are rated to withstand 300%.
Diverse needs in the market
Control Techniques knows that machine OEMs are an individualistic and demanding lot. Some have their own control system, and only want a drive; others want a drive with a limited degree of onboard control, such as indexing; still others want a complete control system integrated with the drive. To satisfy their needs, CT offers Digitax ST in four platforms (from left to right): Base, Indexer, EZ Motion, and Plus.
For further customisation, each accepts two ‘Solution Modules’ from CT’s range of 23, originally developed for the Unidrive. These SMs provide fieldbus, encoder, and I/O options The latest SM is a high density 32 channel I/O module. The unit on the far right, the Plus, has two option modules installed. The gray one in front is for DeviceNet communications and the green one on top is an encoder input. It also has the optional keypad installed at the top front of the unit. Another feature borrowed from the Unidrive is the SmartCard, a credit-card size memory that stores parameters and motion programs. It is protruding from its slot at the top front of the Base unit.
The Base model is just that: a basic drive for OEMs who have their own PC or PLC, and can connect through EtherCAT or with the standard 16-bit analogue signal. SERCOS will be a future option.
The Indexer is designed for simple stand-alone applications such as high speed point-to-point positioning. It uses Sequential Function Chart (SFC), which is included with the drive commissioning software, CTSoft. The interface allows users to configure a range of motion commands such as homing and various index moves. Typical applications include indexing tables, fast conveyor positioning, cut-tolength lines, punching or dispensing machines and transfer units.
The EZ Motion unit uses PowerTools Pro PC programming software to guide the user through the drive, I/O and motion configuration for many indexing and synchronised motor applications. Motion configurations such as travel limits, queuing and gearing are easily achieved within the PowerTools Pro software using easy to complete forms and drag-and-drop functionality. Users can quickly and easily achieve a precision servo solution for indexing tables, pickand- place, packaging and high-speed labelling machines, dancer arm loop control and rotary knife control.
Top of the range is the Digitax ST PLUS featuring a full functionality motion controller optimised for high performance machine cells requiring drive-to-drive networking, cam profiling and synchronised motion (including virtual master). CT has aimed it at complex operations such as printing and packaging machines, synchronising conveyors, flying shear or rotary knife cutting, and so forth.
The on-board drive-to-drive networking links multiple axes for distributed control. The advanced motion features are configured using SyPT Pro, an IEC6113-3 style development environment.
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