Motion control is one of those technologies that have always interested me. Back in junior high school in the 1950s I built a robot from Boy's Life magazine. The Gizmo, an assemblage of tin cans and Erector Set motors, was impressive---but it lacked the kind of servo motor control that today's robots routinely sport.
Times have changed. If I wanted to duplicate the Gizmo today, I'd have lots of processor-based resources to choose from. That also applies to the development of industrial and scientific motion control systems. That's where National Instruments's (NI) new products come in.
NI's three hardware card-level products work in conjunction with the software mentioned in the press release on the left. In addition to Model UMI-7774 and Model UMI-7772 cards mentioned in its press statement, NI also has a UMI-7764 plug-in.
All of these PXI/CompactPCI products give you a straightforward way to connect up motion control hardware and associated feedback signals. In fact, only a single cable is needed from the motion controller one of the NI UMI cards to handle all I/O signals for all axes of motion.
Wiring connections are made on screw-terminal strips. Any UMI product is exactly what the name confers: a universal motion interface with discrete wiring hooks to third-party amplifiers, drivers, and power electronics.
By dividing signals into per-axis and function-specific connections, NI's UMI interface also makes it easier to connect motion control hardware such as power amplifiers, optical and mechanical encoders, and limit switches. For optical encoders, the UMI products work at up to 20-MHz quadrature encoder rates. Here's how a typical system might be configured.
Click for larger system block diagram
Significantly, NI offers options for interfacing to a variety of motors. With these options you can interface to 2-phase stepper motors with 4-A peak current demands, for example. You can just as readily interface to 5-phase stepper motors, or stepper motors that are outside the range of NI MID Series of drives.
The MID Series include built-in power supplies and active cooling, as well as host bus power monitoring and emergency shutdown features. NI's MID drives route all motion drive and motion I/O signals through the units, providing all of the features of a universal motion interface wiring module with the enhancements of a powered motor driver. Products are available as DC-brush servomotors that pull up to 10-A, for example, or for DC brushless, AC, and other types of servomotors. NI supports motors outside the range of its MID Series drives, too. In all cases, the UMI interfaces serve to simplify connections to these products.
The UMIs also pack a number of safety features. For example, there's a host PC power monitor that inhibits the motion driver if the host PC loses power during motion control. The UMI monitors the +5-V power supply line in the controller PC and activates inhibit signals if that voltage goes out of tolerance. Speaking of 5-V TTL levels, these cards are also compatible with TTL (as well as differential) encoders.
Let's look a bit more closely at the UMI-7764. Priced at less than $300, it handles four axes of motion, accommodating single-ended or differential TTL-level inputs. Because these products are typically sited in noisy electrical environments, the UMI-7764's encoder and trigger inputs also include noise filters (with a 100 ns RC time constant). The card's Inhibit inputs and analog inputs also have noise filtering circuits.
NI also supplies two 5B Series power supplies that make it easier to apply the UMI-7764 to motion control systems. One 5B delivers +5-V DC at up to an ampere, and it operates from 115-Vac mains. It's priced at about $180. For heavier motors, NI has a 5B Series power supply that also dishes up 5-V but at up to 5 A. It sells for under $500.
For their parts, the new UMI-7774 (priced at less than $700) and UMI-7772 ($600) cards use optically isolated inhibit trigger inputs that can handle up to 30 volts of input signal. Decrement and reverse polarity protection is also ensured. General purpose I/O and axis-inhibit outputs are also optically isolated. The cards include eight current-sinking inputs and eight current-sourcing outputs. Both the UMI-7772 and UMI-7774 interfaces use subminiature-D-style connectors. They connect to NI motion controllers using an optional Type SHC68-C68-S cable that costs and additional $150.
NI Motion Bits
It's worth noting that the latest NI-Motion driver software also offers LabVIEW VIs (virtual instruments). It also gives you firmware updates, and LabVIEW example programs to help you get started. NI-Motion driver software also offers DLLs and example programs for developing motion control applications with other development packages such as Measurement Studio, LabWindows CVI, or other programming languages.
Ni also has a package called NI Motion Assistant. It uses LabVIEW code generation to help develop LabVIEW motion control applications. Lastly, NI-Motion works with Windows 2000, Windows NT, and Windows XP, but Ni can assist you in porting it over to VxWorks, Linux, or other operating systems as well.
Click for larger screen image
Altogether, these software products make it relatively easy to select a motor and control components for an application. Which motion controller you choose depends on your application (i.e. general-purpose point-to-point motion, or circular movement or vector movement). Once you delineate what your unique system needs, these UMI products and software should streamline the selection process, and ensure a high degree of success in implementation.
For more details, contact National Instruments, 11500 No. Mopac Expwy., Austin, Texas 78759-3504. Phone: 512-683-0100. Fax: 512-683-8411. NI's Web site.
Now, just where did I store those old Erector Set parts?