How SRCI allows programming robots

Integration of programmable logic controllers and robots has become standardized. After I wrote about standard robot command interface (SRCI) as a means for Universal Robots to increase its interface capacity with programmable logic controllers (PLCs), I learned from Profibus and Profinet International (PI) that SRCI has been around for a while. Continuous education is key, regardless of your specialty.

Thus, the question arises, what is SRCI? When was it developed? How widely used is it? Is it instrumental in the new ideas of automation, as far as merging with software-defined automation? If traditional object-oriented techniques are implemented in PLC programming, can this optimize interfaces?

The more complicated systems become, it is critical to have smooth interfaces between devices that share space, such as the PLC and the robot. Let us begin by taking a deeper look into SRCI.

Standard Robot Command Interface (SRCI)

According to PI, “SRCI is an open standard for programming and operating robots in a PLC environment. It enables standardized programming and operation of industrial and collaborative robots, regardless of the PLC or robot manufacturer. SRCI accomplishes this by standardizing the communication between the robot controller and the PLC.”

Picture a handshake not unlike in network protocol frameworks where the PLC is a client to the robot controller. The client sends out a command, such as “Move 1.” The command “Move 1” includes parameters such as location to move to, speed to move at and whether it is a linear movement or an arc. The robot controller receives the packet or message frame with the command and parameter, does a check and says OK. The robot controller interprets the command, executes and sends feedback to the PLC.

Take another step outside the controllers, and the commands are coming from the user program and then being executed by firmware on the robot side. This ability to integrate robot commands, regardless of manufacturer of PLC or robot has been instrumental for growth in the robot market.

Development of SRCI

Around 2015, an engineer suggested that, if robot interfaces were standardized, then PLC programmers could directly program robots from the PLC. PI ran with the idea, and the open standard was created. It is an open, vendor-neutral protocol that works over Profinet. Currently there are more than 115 robot functions covering motion, state reporting and safety integration.

By 2024, there were 28 companies participating and several launches of products that were implementing SRCI. Universal Robots and Yaskawa were two of the first to get on board. Make no mistake: It is a market plus to have SRCI capability.

How does SRCI help integration?

SRCI makes integration simpler, and it enables cross-vendor utilization. This equates to reduction in costs and wider market reach based on one thing: usability. It’s no different than PLCs, in that if the field devices are compatible then the PLC controller can be changed out. Why restrict the automation architecture based on robot brand? The PLC can stay as the conductor in the system with SRCI. Return on investment is improved, and the shift comes back to PLC-centric, which means one specialist with a broad toolbox as opposed to two.

Get your subscription to Control Design’s daily newsletter.

How does SRCI improve programming techniques?

SCRI improves the operability of software-defined automation. Industrial automation is using more object-oriented structures in coding than previously. SRCI makes it easy to define a class structure in PLC code to allow a robot to be represented by a function block. Structure of a class is defined by attributes, methods, constructs, destructs and access specifiers. A robot class can be defined so that it can interface directly to the parameters called out in an SRCI framework as an instance of that class in the form of a function block. This means code is repeatable.

One routine can be called robot, and that routine can call the methods to enable the robot, initialize, reset, jog, stop, move absolute, monitor inputs, monitor position cycle, set dynamic limits and load data. All of this can be built by the programmer that understands the robot interface and then inserted into PLC code with the proper tie-ins so that the PLC may use the robot as a tool. This happens within the boundaries of IEC 61131, which is the international standard for PLC programming.

How does the SRCI get implemented? The integrator buys the robot with the option of using SRCI. Then the interpreter for the SRCI is normally free. An example is MotoLogix from Yaskawa. Yaskawa requires a board to communicate to be bought in the robot controller setup. Then there is software provided to interface with Rockwell Automation or Siemens or Beckhoff, depending on the brand. Then the software must be set up accordingly so that the inputs and outputs and communications to the robot controller may be seen in the PLC.

Under the hood is the SRCI. On top is the PLC interface and the object-oriented code that makes PLC programmers’ lives easier.

Also, the robot still gets commissioned the same way, in that controls engineers and technicians still need to validate I/O for the PLC side and the robot side and need to validate all the interfaces and the functionality.

The teach pendant may not be necessary, but the PLC programmer will most likely want an HMI view for the robot control and the maintenance person will still appreciate the teach pendant.