PCbus motion controller boosts SMT placement performance: The eight-axis servo control used inside Intelliplace's new placement machine for surface-mount PCB assembly is based on a single NextMove PCbus module. The machine's designers selected this controller primarily because of the way its onboard 32-bit digital signal processor allows the motion control part of the system to be off-loaded from the higher-level Windows man-machine interface, for superior performance. They also appreciated the library of C software utilities for the board, which helped the company bring the machine to market in well under a year.

The use of PC architecture is crucial to Intelliplace's design concept, as it gives users a very friendly and flexible means of programming and configuring/operating the machine - an important benefit as manufacturers adopt smaller-batch and just-in-time manufacturing strategies. But this also posed a potential problem, as Windows is not optimized for deterministic real-time response.

When the machine's designers began looking for a suitable PC-compatible module to manage real-time movement, they could find only one system which had the intelligence to off-load this complex control from the host PC - Baldor's NextMove. Other PCbus motion boards relied on the host PC CPU to handle sequencing, posing major software response issues.

Intelliplace's designers were already familiar with Baldor's Mint interpreter from experience with a previous product, and liked the way it simplified software development. But for this new machine, they needed to squeeze as much performance as possible from the board to optimize placement rates, so they were pleased to find a Mint-compatible library of C language routines as well.

"The C library was a big plus for us during design, providing efficient commands for every motion function we needed" notes Intelliplace's Senior Development Engineer Iain Scott. "Without this support, the software development task would have been immense - adding months to project timescales".

The new mid-range machine - designated the DHM-120 - offers users a typical placement speed of 6,000-6,500 components/hour for conventional mixed-device PCB assembly tasks, but with up to 9,000+ components/hour rates achievable on more restricted operations.

Although the high movement speed is attributable largely to the power of the NextMove controller, the product's CAN (Controller Area Network) bus interface also makes a valuable contribution. Controlling the machine's dual, five-tool heads, necessitates a significant amount of digital I/O, to read position sensors and actuate solenoids. The availability of CAN allowed Intelliplace to simplify the system by siting this I/O directly in the head, without the usual penalty of complex, heavy wiring. Further digital I/O is also required to control the machine's PCB transfer mechanisms and feeders, and here, CAN allowed Intelliplace to site the I/O directly at the point of use - saving wiring and a significant amount of assembly labour.

The design team also sees CAN coming into play in the design of accessories. In particular, the team is developing a 'waffle' tray sequencer for feeding very large components. They expect to use new-style CAN-compatible drives to control the motion of this product - providing users with more cost-effective upgrade options.