Analysis and optimization of communication protocols between motors and drives

Improvements in the design of industrial motors and their communication with drives and other systems can help engineers succeed with industrial machines and applications.

Designing and deploying motor drive systems helps improve automation efficiency and provide information to key parts of the production process. Industrial communications between motors and drives and other devices and systems typically use standards-based protocols such as EtherCAT, EtherNet/IP, and Profinet.

Three experts from communication protocol organizations: Michael Bowne, Executive Director of the PI User Organization North America, Bob Trask, North American Representative of the EtherCAT Technology Group, and Paul Brooks, a member of the Distributed Motion and Time Synchronization SIG of the ODVA organization, introduced to us how engineers can optimize motor drive systems and improve industrial motor communication, operation and safety.

01

Motor Selection Criteria

Bob Trask, North American representative of EtherCAT Technology Group, believes that good motor communication helps with drive setup. First, you need to choose the motor type, encoder and load type, current, power, maximum speed, reference speed and other relationships. The next thing to consider is the mode. Do you choose to use positioning mode? Is it based on position control? Or is it based on speed, torque-based motion or current-based motion? Do you prefer centralized motion control or distributed motion control? Centralized motion control eliminates a lot of complexity.

Cycle Synchronous Speed ​​is a CANopen term that I find increasingly used. The CiA DS402 Device Profile for Drives and Motion Control is a protocol used by EtherCAT. CiA DS402 provides smoother positioning in each cycle. You can select a different value for cycle monitoring.

There is a huge and growing interest in motor drive safety. Integrated safety is the biggest consumer of data and is becoming more widely integrated with drives. The exchange of predictive maintenance information is also increasing, where users can try to predict problems before they occur.

Figure 1: The types of information that motors and drives communicate include process data, safety, configuration, diagnostics, analytics, time synchronization, vendor-specific functions, and control models/modes.

02

Analysis and optimization of electric motors

Paul Brooks, a member of the Distributed Motion and Time Synchronization SIG of the ODVA organization, believes that the cornerstone of motion control is the real-time exchange of process data between the controller and the drive, including speed mode, position mode, position command, speed command, torque command, feedback position, speed torque and status information.

The combination of a motor and a drive is a way to physically move something. Ensuring operator safety is more than just stopping the motor; it involves operating the motor and motion control system in a safe manner, at a safe speed, with a safe torque, etc. Configuration, diagnostics, and analysis are key. Information can be obtained about the drive, the motor, and its effect on the load.

Operators can use this analytical information, often through artificial intelligence and machine learning, to improve short-term real-time control and long-term process optimization of the system. This includes identifying deterioration in the drive-motor pair, as well as deterioration in the mechanical load to which it is connected. Data analytics accounts for the largest portion of the growth in data flows. Time synchronization is a key network service that allows coordinated motion control to ensure that drives and motors have the same understanding of time. Vendor or protocol-specific information is another important data set.

ODVA provides two separate modes of operation in motion control, a simple I/O data block that is standardized to provide interoperability between vendors, and a simplified interface that typically transmits speed commands from the drive. There is a higher performance motion interface between the controller and the drive called CIP Motion. This application profile provides a collaborative view of a distributed model that has a better centralized model.

03

Optimizing Motor Drive Communication

Typically, a drive has many parameters that need to be configured and parameterized. "You need to send setpoints from the controller to the drive," says Michael Bowne, executive director of the PI User Organization North America. The controller can be a programmable logic controller (PLC) or an industrial PC, or it can be a dedicated controller for the motor.

The drive then sends back actual values ​​such as torque, current, speed, position, setpoint slope and units and other parameters. In Profinet, these interfaces are defined by application classes. Actual values ​​and setpoints (especially actual values) can be sent back from the drive to the central controller, or the drive can communicate with the drive.

Centralized control using Profinet (based on Ethernet). It can be a simple object, such as a pump or fan in a process control application, which is usually configured with a simple open loop drive. There is no feedback, or if there is, it comes from an encoder or servo. Clock synchronization is not required because this is a very simple application. The cycle time is about tens of milliseconds. Other applications may require more complex objects, such as single axis positioning that sends position information from the PLC to the drive.

The servo or encoder provides feedback for closed loop control from the drive to the controller. This is also not synchronized via a clock, as it is single axis, it may not need to be, but the cycle period is about 1 to 10 milliseconds. In the high performance area, multiple axes can be synchronized using multiple positioning clocks.

Feedback is required for sub-millisecond cycle times. This requires the exchange of setpoints and actual values ​​with time synchronization. What works in one application may not be necessary in another high-performance application, and vice versa.

Figure 2: The Tool Call Interface (TCI) is a Profinet feature that is similar to Profidrive’s philosophy of making drive setup as easy to run as possible.

04

Assisting smart manufacturing

In smart manufacturing, self-organizing production is achieved through the reuse of modular machines. A machine may have multiple different functions and can be placed in multiple different locations in the production unit. Brooks said that the machine needs to be able to determine where it is and where to get the required recipe. All manufacturers are working hard to achieve lightweight factories to improve efficiency and reduce labor costs, and better ensure the safety of the workforce, especially when the number of available workers is reduced.

Driven by additive manufacturing, 3D printing, and more, mass production is beginning to make its way into the consumer packaging industry. In smart manufacturing, digital twins predict the operations we expect. Digital twins bring new disciplines to the engineering field. Data scientists work with subject matter experts to turn abnormal conditions into normal operations, better reporting, better system monitoring, and better overall monitoring. Remote workers can bring expertise to machines without redeployment.

The development of motor drive communication interfaces helps improve productivity, safety and sustainability. It helps to run motors more efficiently to reduce energy costs and determine why motor failures occur. Predicting failures can reduce costs and reduce the time of the worst type of downtime - unplanned downtime. Advanced diagnostics provide maintenance personnel with more information before intervening in the system, thereby reducing intervention time, which helps improve productivity and operational efficiency. At the core of sustainable development is improving production efficiency, thereby reducing the overall manufacturing cost to the environment.

05

Convenient driver configuration and analysis

Bowne believes that smart manufacturing is also about ease of use, making it easier for people to complete tasks and freeing up time for application analysis to help predictive maintenance, not just optimization. The Tool Call Interface (TCI) is a feature of Profinet that is similar to Profidrive's philosophy of making drive settings as easy to run as possible. The tool call interface integrates the drive supplier's commissioning tools directly into the PLC engineering, for example, IBC or devices that control the network. End users can use the familiar PLC engineering tool interface in the PLC setup and access all the functions of the supplier's commissioning tool.

This makes the drive easier to set up and makes it easy to store all configuration data in the same place (in the PLC project), avoiding the need to go back and forth between the commissioning tool and the PLC project. This is handled through a standardized application program interface (API). Many drive vendors with commissioning tools have written code that matches this API so that the tools can be used in the PLC project.

Information models help drives run faster and easier, especially the OPC UA companion specification. OPC UA takes application profiles like Profidrive one step further. Profidrive configures all parameters in a standardized way so they always look the same when transferred between drives, motors and controllers. Once the plant is running smoothly, how can you save time preparing and cleaning data for analysis?

OPC UA plays an important role in providing a powerful information model to make it as simple as possible. As IT/OT continue to converge, users want more drive data at the edge. Profidrive's companion specification maps drive parameters into the OPC UA information model. Smaller manufacturing companies that have not achieved IT/OT convergence may need to use multiple protocols on the same line or need to do some basic analysis, and OPC UA can help with this.