Product advice: Why, what, how of new motion control drive
New digital drives are compact, PCB-mountable modules that provide high performance motion control, network connectivity, and power amplification for brushless dc, dc brush and step motors. The miniature devices are for creating embedded control and automation applications, according to a company with a Control Engineering Engineers’ Choice Award product.
- Learn the design drivers for miniature, high-performance motion controls.
- How to improve motion performance and positioning accuracy using embedded digital drives.
- Understand the build versus buy decision of motor drive technologies.
Compact digital drives combine an integrated circuit and digital amplifier to create an ultra-compact package that can be mounted on a printed-circuit board (PCB). In addition to advanced servo and step motor control, such drives can provide S-curve point to point moves, plenty of general-purpose digital and analog input/output (I/O) and sin/cos and BiSS-C encoder support. There also is support for expansion CAN and SPI networks in addition to the host network to support a hierarchical network architecture.
Design drivers for miniature, high-performance motion controls
With frequent announcements of smaller motors, controls and sensors used in precision motion control. What is driving these applications is the growing demand for motion control components used in surgical, patient treatment, mobile robotics, drones and battery-powered applications. These trends drive development of motion control technologies to let engineers build systems that use less power, make less noise and take up less space.
As smaller is better for an increasing number of applications when it comes to the motor and amplifier size, closer is better when building machines that use motion control. This is especially true with those that integrate analog sensors such as sin/cos encoders.
How to improve motion performance, positioning accuracy
The reason boils down to two simple principles: shorter signal runs mean cleaner more accurate signals, and shorter signal runs means the servo loop can run faster while still maintaining safe phase margins. Both factors have a major impact on motion performance, with a particular emphasis on positioning accuracy.
While some machine applications will not see big performance improvements from shorter signal runs, systems with smaller motors, and systems utilizing newer generations of encoders such as sin/cos encoders striving for ultra-high accuracy measured in nanometers or even picometers will. For spindles that need to maintain high position or velocity control accuracy, fast servo loops and clean sensor signals also can make a big difference.
This is because these devices do all the heavy lifting associated with the machine control function. They can run user application code, generate motion profiles, handle servo positioning, and drive the motor with an on-board amplifier. These devices also offer multiple interfaces such as serial, CAN and Ethernet. Most importantly, they are small, often 3 to 5 cm on a side.
While not new, PCB-mounted motion control modules have shrunk in size while increasing in power output over the last 10 years. Because of the convenience, it seems these devices are here to stay and will continue to shrink in size and expand in capability in the future.
Finally, perhaps the biggest impact of miniaturized controls is it allows the machine architecture to be re-organized. Moving from centralized motion to local/embedded motion brings advantages of greater signal integrity, faster servo loops, less EMI, increased reliability, and lower cost.
Build versus buy decision of motor drive technologies
Mobile and portable motion applications are exploding in popularity due to the demands of patient treatment devices, mobile diagnostic equipment, and battery-operated medical devices. Design engineers are being asked to build systems that take up less space, use less power and still provide higher performance.
For the design engineer building an application specific motion control board using these plug-and-play devices, the task is more one of interconnecting than of actual circuit design. Whereas a full-blown motion board designed from ICs would often require a 10+ layer PCB and serious digital and analog design skills, a board made with these plug-and-play motion control modules is often a 2 or at most 4-layer board, and the design task focusses on selecting connectors and specifying the board’s form factor.
With these all-in-one devices building a fully-custom board is a snap; a simple 2 or 4-layer interconnect board can connect multiple drives.
KEYWORDS: Miniature embedded drive advice, Engineers’ Choice Awards
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