gRPC via Python

To work with gRPC in Python, you need to install the following packages:

sudo python3 -m pip install grpcio

python3 -m pip install grpcio-tools

Then you can automatically generate Python code with that command:

python
python3 -m grpc_tools.protoc -I./protos --python_out=. --pyi_out=. --grpc_python_out=. ./protos/prc.proto

This gets you the following three files:

prc_pb2_grpc.py

prc_pb2.py

prc_pb2.pyi

Along in the folder is the prc_localhost.pem certificate for the SSL encryption. It is included in the example project.

Import the following libraries for the sample

python
import logging
import os
import time
import threading
import grpc
import prc_pb2
import prc_pb2_grpc

Next, set up the path to the *.pem certificate and establish the GRPC channel

python
print("Getting certificate from same folder as the python code...")
__location__ = os.path.realpath(
os.path.join(os.getcwd(), os.path.dirname(__file__)))
with open(os.path.join(__location__, 'prc_localhost.pem'), 'rb') as f:
    credentials = grpc.ssl_channel_credentials(f.read())

print("Connecting to https://localhost:5001...")

with grpc.secure_channel("localhost:5001", credentials) as channel:
    stub = prc_pb2_grpc.ParametricRobotControlServiceStub(channel)

Ping the PRC Server and choose a unique ID for your robot

python
response = stub.SendPing(prc_pb2.Ping(payload="", time_ms=10))
robot_id = "PRC_Test"

You can then setup your robotic system. The robot driver class and preset robot class reference existing drivers/robots in PRC.

python
setup_robot_reply = stub.SetupRobot(
	prc_pb2.SetupRobotRequest(
	    client_id=robot_id,
	    software_version="0.1",
	    robot_setup=prc_pb2.Robot(
	        friendly_id="KUKA KR10",
	        robot_driver_class="KUKA.KSS_KRL_Driver",
	        preset_robot_class="KUKA.KUKA_KR610R11002",
	        initial_base=prc_pb2.Base(
	            base_id="0",
	            base_frame=prc_pb2.CartesianPosition(
	                cs=prc_pb2.CoordinateSystem(
	                    origin=prc_pb2.Vector3(
	                        x=0,
	                        y=0,
	                        z=0
	                    ),
	                    x_axis=prc_pb2.Vector3(
	                        x=1,
	                        y=0,
	                        z=0
	                    ),
	                    y_axis=prc_pb2.Vector3(
	                        x=0,
	                        y=1,
	                        z=0
	                    )
	                )
	            )
	        ),
	        tool_dictionary={
	            "0": prc_pb2.Tool(
	                tool_id="0",
	                tool_type=prc_pb2.FrameType.FIXED,
	                tcp=prc_pb2.CartesianPosition(
	                        cs=prc_pb2.CoordinateSystem(
	                        origin=prc_pb2.Vector3(
	                            x=0,
	                            y=0,
	                            z=0
	                        ),
	                        x_axis=prc_pb2.Vector3(
	                            x=1,
	                            y=0,
	                            z=0
	                        ),
	                        y_axis=prc_pb2.Vector3(
	                            x=0,
	                            y=1,
	                            z=0
	                        )
	                    )
	                )
	            )
	        }
	    )
		)
	)

In order to get feedback, we establish the feedback stream and spin up a thread for it.

python
feedback_stream = stub.SubscribeRobotFeedback(
    prc_pb2.SubscribeRobotFeedbackRequest(
        id=robot_id,
    )
)
    
print("Starting separate thread to manage the feedback stream coming from PRC")
stop_event = threading.Event()
feedback_thread = threading.Thread(target=thread_feedback, args=(stop_event, feedback_stream,))
feedback_thread.start()

The relevant thread looks like this.

python
def thread_feedback(stop_event, feedback_stream):
    for feedback in feedback_stream:
        if stop_event.is_set():
            break

        assert isinstance(feedback, prc_pb2.RobotFeedback)
        field = feedback.WhichOneof('data_package')
        if field == "heartbeat_data":
            print("Feedback thread: Received heartbeat data")
        elif field == "robot_state_data":
            print("Feedback thread: Received robot state data")
        elif field == "settings_data":
            print("Feedback thread: Received settings data")
        elif field == "ping_data":
            print("Feedback thread: Received ping data")

You can now define your movements and group them in MotionGroup objects.

python
ptp_motion_1 = prc_pb2.MotionCommand(
    axis_motion=prc_pb2.AxisMotion(
        target=prc_pb2.JointTarget(
            axis_values=[-45, -90, 90, 0, 0, 0],
            speed=[0.1]
        )
    )
)

ptp_motion_2 = prc_pb2.MotionCommand(
    axis_motion=prc_pb2.AxisMotion(
        target=prc_pb2.JointTarget(
            axis_values=[45, -90, 90, 0, 0, 0],
            speed=[0.15]
        )
    )
)

ptp_motion_group = prc_pb2.MotionGroup(
    commands=[ptp_motion_1, ptp_motion_2],
    interpolation="C_PTP",
    motion_group_type=prc_pb2.MotionGroupType.PTP
)

Next, put the motion groups into a task. You get the default robot_settings from the initial SetupRobot call. As they are a dictionary, you can edit them easily.

python
task_reply = stub.AddRobotTask(
    prc_pb2.AddRobotTaskRequest(
        id=robot_id,
        robot_task=prc_pb2.Task(
            name="Task",
            type=prc_pb2.TaskType.SIMULATE_AND_EXECUTE_TASK,
            payload=[prc_pb2.TaskPayload(
                motion_group_task=ptp_motion_group
            )]
        ),
        robot_settings=prc_pb2.Settings(
            settings_dictionary=setup_robot_reply.robot_settings.settings_dictionary
        )
    )
)

Among the output of the task_reply is e.g. the code object, containing the code to run on the robot.

You can go through the simulation through the GetStimulatedRobotState call. In the example below, it iterates by 4% every 400ms.

python
i=0
while i < 100:
    i+=4
    robot_state = stub.GetSimulatedRobotState(
        prc_pb2.GetSimulatedRobotStateRequest(
            stream_update=False,
            id=robot_id,
            normalized_state=i/100.0
        )
    )
    axis_values = robot_state.actual_axis_position.axis_values
    print("At factor " + str(i/100.0) + " the robot is at A1: " + str(axis_values[0]) + " A2:" + str(axis_values[1]) + " A3:" + str(axis_values[2]) + " A4:" + str(axis_values[3]) + " A5:" + str(axis_values[4]) + " A6:" + str(axis_values[5]) )
    time.sleep(0.4)

The full code is available here:

PRC.Integrations

jbraumann • Updated Apr 29, 2025