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Did You Know? Industrial Networking, Part II

May
02
by Jeff Kordik

If you read Ken Doner’s Industrial Networking article in the March newsletter, you know that Applied Motion is big in real time connectivity. This month, we show examples. The device below is a linear actuator driven by an Applied Motion STM24QF integrated drive+motor. The STM24 accepts Modbus commands from an HMI over RS-232.

Commanding motion over Modbus is easy. To control speed, acceleration, deceleration and distance, simply create some HMI numeric data entry displays and map them to the STM24’s internal Modbus registers, as seen in the table below. Then create a GO button and instruct it to send the constant that represents the type of move you wish to occur to the STM24’s command register (40125). A sample HMI position command screen is shown below the chart.

It is also useful to monitor the motor drive from the HMI. A monitor screen is shown above, on the right. Drive status, alarm codes, real time speed and position, and much more can be observed by mapping HMI numeric data displays to the STM24’s Modbus registers in the range 40001 to 40017. Because these registers are arranged in a contiguous block, they can be captured by a PLC in a single data transfer. That simplifies PLC programming and minimizes network overhead. At Applied Motion we are always thinking like a customer, finding ways to increase the value of our products in your application.

All of the information shown here, plus sample programs, can be found in the application notes page on our website.

Now we’re going to shift gears and talk about complex moves. In this age of widespread connectivity, many applications use industrial networks to stream complex move commands to individual motion axes. With Applied Motion drives, this can be done with RS-232, RS-485, CANopen or Ethernet. Applied Motion’s CANopen products include a profile position mode where a set of set points is streamed to the drive in real time resulting in rapid, complex changes in velocity and position, as seen in the plot below where we illustrate the motor’s speed over time.

Not using CANopen? The same complex motion can be achieved by streaming SCL commands to an S or Q drive. For incremental positioning, where you tell the drive where to go relative to where you are, this is achieved by selecting command mode 23 (CM23). For absolute positioning, use CM24.

The velocity is set using the Velocity (VE) command. When you send a new Distance (DI) command, which specifies distance in CM23 or position in CM24, the DI plus VE constitute a new set point to be executed as soon as the current set point move is completed. If a new set point is sent before the current one is completed, the motor will continue to move at the previous speed until the previous distance/position is reached; the motor does not stop. Then the motor will accelerate to the new VE value and the new DI value will be used as the target distance/position. When you run out of set points, the motor decelerates to a stop.

Here’s an example SCL script to command the move shown in the chart. You can try this yourself using our SCL Utility’s scripting window:

CM23
VE8
DI-20000
%82
VE3
DI-20000
%300
VE3
DI20000
%300
VE8
DI30000
%200
VE7
DI-20000
%300
VE5
DI-20000

There’s plenty more to tell, but we’re out of space, so please check back next month for another Did You Know. And be sure visit our website for past articles.

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