Here's an idea: Use an inexpensive PC to control the axes of a robot but do so in a way that avoids the cost of a Windows operating system. This is the model Automated Assemblies Corp., Clinton, Mass., (aac-robot.com) followed in fielding a new robot for the injection-molding industry. Although PC-based controls are widely used in motion control, “We've been leery of them because of Windows,” says AAC Product Development Manager David Lee. He didn't like the licensing fees involved or the need to stay current with new versions of the operating system, which could involve significant effort over the average 10-yr life of an industrial robot.

The way around this dilemma uses the Linux open source operating system. AAC's Raptor Series robots handle motion control and work-cell functions through a PC-based platform from Motion Engineering Inc., Santa Barbara, Calif., (motioneng.com). The real-time version of Linux running on the MEI board “gives us more control of our destiny,” explains Lee. “We can customize the kernel as necessary. Plus, relying on an outside supplier for motion control lets us be experts in building robots and not in building motion platforms.”

Off-loading motion control to a card also let AAC use a less-powerful PC to handle the balance of work-cell chores. Besides serving as an operator terminal, the PC interacts with I/O through the same interface that handles servo axes. AAC also uses this capability to give custom molders a way to quickly change their production setups, thus shortening the turnaround for new jobs. “An open mold is considered downtime,” explains AAC president Steve Braig. “The goal is to have the mold full and making product, so we want to reduce the cycle time molds are open. One solution is to make robots go faster.”

An XMP SynqNet-PCI network and controller handle all servo axes and I/Os. XMP controllers use digital signal processors to manage dedicated motion. A map architecture works over the computer PCI bus for handling tasks between host and controller. Motion programming takes place by MPI, an ANSI-compatible object-oriented C/C++ motion-programming library that works with other SynqNet controllers. (Other programming environments include ActiveX and MatLab/Simulink, which are accessed by plug-ins.) MPI is platform-independent. In addition, it supports CANOpen, so one programming interface handles motion and CAN I/O. Daisy chains and ring topologies network the controllers. Ring topologies let “self-healing” fault tolerant operations work around cable faults between nodes. Motion continues by duplex communication from the controller.

The SynqNet network is based on IEEE 802.3. Only one cable runs between controller and drives, so wiring and debugging could be done on a prototype in a matter of hours. And the small size of the controller lets it sit close to motors, further reducing the amount of cabling. The network handles torque-update rates of 48 kHz, downloads configuration files and firmware, and makes it possible to monitor cells remotely by Ethernet.

SynqNet supports up to 32 tightly synchronized high-performance axes, keying on applications with end-of-tool servo requirements. AAC developed its own graphic user interface for a drag-and-drop touchscreen to control and teach the robot routines, as well as other equipment in work cells such as vision-inspection equipment, and conveyors.

AAC also developed routines which let the controller adjust speed and motion trajectories based on type and weight of parts being taken from the molds.