diff --git a/script/RobotTCP.py b/script/RobotTCP.py
index fab2f02..828f811 100644
--- a/script/RobotTCP.py
+++ b/script/RobotTCP.py
@@ -236,8 +236,8 @@ class RobotTCP(TcpDevice, Stoppable):
         return self.evaluate("setMoveId(" + str(id) + " )")
 
     def get_joint_forces(self):
-        robot_tcp.evaluate("getJointForce(arr)")        
-        return robot_tcp.get_float_arr(6)
+        self.evaluate("getJointForce(arr)")        
+        return self.get_float_arr(6)
 
     def movej(self, joint_or_point, tool, desc):
         return self.eval_int("movej(" + joint_or_point + ", " + tool + ", " + desc +")")