Get the robot position

This article shows how to read the current position of a Staubli robot from a PC, in C# or Python, on a CS8 or CS9 controller. It compares the three ways that the SDK offers, then gives a complete program that prints the position of a tool 10 times per second.

Prerequisites

• The PC reaches the controller, and the SDK is connected: see Connect to your robot.
• Nothing else: reading the position does not need the remote mode, the power or a VAL 3 program.

Which method to choose

• For a Cartesian position, GetCurrentCartesianJointPosition is the right choice: it gives the joints too, in the same request.
• Pass a tool to get the position of the tool center point instead of the flange, and a frame to get it in the frame of your part instead of the world frame.
• ForwardKinematics returns a full frame with its rotation matrix, and the configuration of the arm. Use it for positions that are not the current one.

Example

using UnderAutomation.Staubli;
using UnderAutomation.Staubli.Soap.Data;

public class HowToGetPosition
{
    static void Main()
    {
        
        var controller = new StaubliController();
        controller.Connect("192.168.0.254");

        // Tool center point, 150 mm along Z of the flange
        var tool = new CartesianPosition { Z = 0.150 };

        // Read the position 10 times per second, for 5 seconds
        for (int i = 0; i < 50; i++)
        {
            CartesianJointPosition position = controller.Soap.GetCurrentCartesianJointPosition(robot: 0, tool, frame: null);
            CartesianPosition tcp = position.CartesianPosition;

            // Meters to millimeters, radians to degrees
            Console.WriteLine(
                $"X={tcp.X * 1000:F1} Y={tcp.Y * 1000:F1} Z={tcp.Z * 1000:F1} mm, " +
                $"J1={position.JointsPosition[0] * 180 / Math.PI:F2} deg");

            Thread.Sleep(100);
        }

        controller.Disconnect();
        
    }
}

The SDK gives meters and radians. The program converts them to millimeters and degrees to print them.

Polling period

Each read is one request to the controller. Its duration depends on the network and on the load of the controller: measure it on your cell (with a Stopwatch in C#, time.perf_counter() in Python) before you choose the period of your loop. Do not read faster than you need.

Troubleshooting

• The Cartesian position does not match the pendant: the pendant shows the position of the current tool in the current frame. Pass the same tool and frame to GetCurrentCartesianJointPosition.
• InvalidRobotIdCode: the robot argument does not match an arm of the controller. Use 0 for the first arm, and see GetRobots().
• Values look too small: they are in meters and radians. Multiply by 1000 for millimeters, and by 180/π for degrees.

What to read next

• Position: the reference of the position methods.
• Kinematics: forward and inverse kinematics.
• Move the robot from a PC.