It should come as no surprise that PROFINET also supports motion control applications with drives and motors (sometimes also referred to as VFDs – Variable Frequency Drives) as these are used in most modern automation systems. Motion control support comes with PROFINET technology from three main aspects:
1.) The ability for scalable real-time control depending on the drive application
2.) Improved determinism through bandwidth utilization and scheduling
3.) PROFIdrive application profile option
Next, we’ll describe these aspects in a little more detail.
First, motion control applications can have different requirements depending on the application:
|Drive Technology||Application||PROFINET mechanisms supported|
|Drives with fixed and variable speed||Pumps, Fans, Compressors, Transport, etc.||Real-Time (RT) or optional IRT clock sync|
|Single axis controllers||Moving, resetting, positioning, etc.||Real-Time (RT) or optional IRT clock sync|
|Multi axis controllers||Packaging, Printing, Milling, etc.||IRT clock synchronization is required|
As our table points out, for most common VFDs and single axis controllers the drive is operated as a standard PROFINET IO Real Time (RT) device. Each device (and controller) operates on its own local clock and does most of the interpolation and processing locally. Also, the device simultaneously provides feedback to the controller. With high-speed motion applications such as multiple axis synchronizations and closed loop / dynamic servo control, PROFINET Isochronous Real Time (IRT) has the ability to synchronize all the nodes so there can be precise determinism and reduced jitter. All the drive coordination and control is then done via the PROFINET network. Therefore, PROFINET provides functionality for even the most demanding motion control applications with scalable solutions.
Bandwidth Reservation and Scheduling
The second aspect PROFINET adds to coordinate multiple drives is bandwidth reservation and scheduling. This makes Ethernet truly deterministic and ensures the motion control applications will function properly. To accomplish this, it uses IEEE1588 V2 clock synchronization to reserve a portion of the bandwidth and a time period phase just for IRT, and another open period phase for other traffic such as RT or TCP frames. This guarantees the IRT traffic will continue to function irrespective of other network traffic.
Another addition is scheduling for high performance. The IO controller knows the network topology and what devices are part of the configuration, including their data sets. Therefore, when setting up the devices, the controller notifies them of the precise time during the IRT phase when they are sending and receiving information, so a schedule is created. This guarantees determinism and ensures the jitter will allow the motion application to work. And usually, in typical IRT applications, the jitter value will be less than a microsecond. Now that is precise!
PROFIdrive application profile
Finally, the last aspect of PROFINET motion control is the addition and benefits of the PROFIdrive application profile. PROFIdrive helps organize the data sets and parameters for drive applications since drives also have different types of data and hundreds of parameters. We’ll cover more in detail about PROFIdrive in our next article.