Get the robot position

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Read the position of a Yaskawa robot from C# or Python: Cartesian position or joint pulses, which method to choose, and a polling loop. Complete program included.

Prerequisites
Which method to choose
Example
Polling period
With the Ethernet Server
From joint angles, without the robot
Troubleshooting
What to read next

This article shows how to read the position of a Yaskawa Motoman robot from a PC, in C# or Python. It gives a complete program that reads the Cartesian position and the joint pulses, then polls the position 10 times per second.

Prerequisites

The SDK is connected to the controller: see Connect to your robot.
Nothing else: reading the position works in teach mode and in play mode, without the remote mode.

Which method to choose

Need	Method	Unit
Where the tool is, to log it or to compute	`GetRobotCartesianPosition()`	mm and degrees, robot frame
A position to send back with `MoveJoints`	`GetRobotJointPosition()`	Encoder pulses per axis
The load of the axes during a move	`GetTorque()`, `GetPositionError()`	Percent, pulses
A position taught in a job	`ReadPositionVariable(n, 1)`	Raw units of the `P` variable
A second robot, base axes	`GetRobotPosition(group)`	Pulses or raw Cartesian values

Example

using UnderAutomation.Yaskawa;
using UnderAutomation.Yaskawa.HighSpeedEServer;

public class HowToGetPosition
{
    static void Main()
    {
        
        var robot = new YaskawaRobot();
        robot.Connect("192.168.0.1");

        // Tool center point in the robot frame: mm and degrees
        RobotPositionCartesianData tcp = robot.HighSpeedEServer.GetRobotCartesianPosition();
        Console.WriteLine($"X={tcp.X:F3} Y={tcp.Y:F3} Z={tcp.Z:F3} Rx={tcp.Rx:F4} Ry={tcp.Ry:F4} Rz={tcp.Rz:F4}");
        Console.WriteLine($"Tool {tcp.ToolNumber}, posture {tcp.Form}");

        // Joints: encoder pulses, one value per axis
        RobotPositionIntData joints = robot.HighSpeedEServer.GetRobotJointPosition();
        Console.WriteLine("Pulses: " + string.Join(", ", joints.Axes));

        // Poll the position 10 times per second for 5 seconds
        for (int i = 0; i < 50; i++)
        {
            tcp = robot.HighSpeedEServer.GetRobotCartesianPosition();
            Console.WriteLine($"{DateTime.Now:HH:mm:ss.fff} X={tcp.X:F1} Y={tcp.Y:F1} Z={tcp.Z:F1}");
            Thread.Sleep(100);
        }

        robot.Disconnect();
        
    }
}

The program:

reads the Cartesian position of the tool, with its tool number and its posture;
reads the pulses of each axis;
reads the Cartesian position every 100 ms for 5 seconds.

Polling period

Each read is one request and one answer over the network. On a local network, a request takes a few milliseconds: measure it on your cell before you choose the period. Read only what you need in a loop: the Cartesian position alone is one request, the position and the joints are two.

With the Ethernet Server

The Ethernet Server reads the same positions over TCP, and also in a user frame or in the tool frame. It also gives the posture of the arm and the temperature of the encoders.

var robot = new YaskawaRobot();
robot.Connect(parameters);
// Joints, in encoder pulses
HostControlJointPositionData joints = robot.EServer.GetRobotJointPosition();
Console.WriteLine($"S={joints.S} L={joints.L} U={joints.U} R={joints.R} B={joints.B} T={joints.T}");

// Cartesian position in the base frame (default), mm and degrees
HostControlCartesianPositionData tcp = robot.EServer.GetRobotCartesianPosition();
Console.WriteLine($"X={tcp.X} Y={tcp.Y} Z={tcp.Z} Rx={tcp.Rx} Ry={tcp.Ry} Rz={tcp.Rz}");

// Posture of the arm and tool of the position
Console.WriteLine($"Front: {tcp.IsFront}, upper arm: {tcp.IsUpperArm}, flip: {tcp.IsFlip}, tool: {tcp.ToolNumber}");

// Same position in the robot frame, or in a user frame
var inRobot = robot.EServer.GetRobotCartesianPosition(HostControlCoordinateSystem.Robot);
var inUser1 = robot.EServer.GetRobotCartesianPosition(HostControlCoordinateSystem.User1);

// With the external axes (Re, Axis8...)
var withExternal = robot.EServer.GetRobotCartesianPosition(HostControlCoordinateSystem.Base, true);
robot.Disconnect();
}

Click to see the full code

From joint angles, without the robot

To compute the position of the flange from joint angles in degrees, or every set of joint angles for a position, use the offline kinematics. The computation runs on the PC, without a connection.

Troubleshooting

The values are all 0: check the control group and the number of axes with GetConfigurationInformation.
The Cartesian position differs from the pendant: compare the frame and the tool. DataType and ToolNumber give the ones of the answer.
The first call fails after a pause: a SocketException means that the controller did not answer before DataTimeoutMilliseconds. Check the network, then call again.

Any question?