Wed 3. Sep 2014, 16:10
Wed 3. Sep 2014, 16:10
Thu 4. Sep 2014, 11:53
Robotica wrote:Firstly, when it comes to the joints of the robot, the stop condition is based on the external force, isn't it?
Robotica wrote:Based on the telemetry information these external forces seem awfully small compared with the limits provided... So my question is: do the torques (NOT external), also provided by the telemetry message, have any effect on the when the stop condition is met? If yes, how do they affect the conditions?
Robotica wrote:Is a StopCondition message published at the same time giving information about the joint that caused the disruption? I see there exists a topic called /euroc_interface_node/stopcondition but no messages seem to be published there. What I did to test this was to simply drive the manipulator to a point where one of the joints exceeded the torque limit provided using the SetStopCondition service, and then check the above mentioned topic but there was nothing.
Robotica wrote:Thirdly, I would greatly appreciate a more thorough insight into the condition operators published within the stop condition message. If, for instance, I choose the operator '|>', which according to the technical annex means "absolute value is bigger than threshold", does it mean the robotic arm can move around until its external torque exceeds the limit I have set for it? At least in some of my tests the robot has been able to continue moving even if the external torque momentarily exceeded the limit set by myself. When, on the other hand, I change the operator to '|<', the robot stops but starts moving again when the limit is set to naught, for example (thus making the external torque greater than the limit).
# - ">" which means value is bigger than threshold
# - "<" which means value is smaller than threshold
# - "|>" which means absolute value is bigger than threshold
# - "|<" which means absolute value is smaller than threshold
Thu 18. Sep 2014, 10:41
Mon 22. Sep 2014, 09:14
Thu 25. Sep 2014, 08:23
Robotica wrote:Working with the SetStopCondition service I also noticed that setting a stop condition for the gripper (tool_force_threshold) leads to some problems. I took this threshold as equivalent to max_gripper_force, which is 200 N.
Robotica wrote:But when I set this condition, the robot would not move at all from its original vertical position, and the MoveAlongJointPath service provided me with the following StopReason:
Stop Condition 7: total force in direction [0.000000, 0.000000, 0.000000] is 1434.191 N |> 200.0000 N, full force vector: [-1.727565, -20395.262286, 141977.770114] at sim_time 2.190
Robotica wrote:As I understand, the stop condition is given the number 7 because number 0 corresponds to the first joint.
Robotica wrote:What surprises me is the immense amount of force measured at the gripper, and I had to ask myself whether it is a realistic value or rather an error within the code... Furthermore, the measurements come straight from the simulation but do not correspond to the values provided by the GetEstimatedExternalForce service either.
Robotica wrote:Additionally, I would like to ask one more thing about the stop conditions. Sometimes, when the robot has picked up an object and is moving toward the corresponding target zone, one of the stop conditions may be exceeded and the robot stops with a jerk. This jerking movement then causes the robot to lose the object and the screen turns red indicating task failure. Why does this happen? Is it because the object hits the robot or a similar reason? On stopping due to a red screen, the MoveAlongJointPath service only provides an empty string as the StopReason, which does not offer any explanation as to why the simulation was stopped.
Robotica wrote:... the service call fails and the following error message is printed:
Setting Stop Conditions failed: /home/devel/euroc/gazebo/challenge2_sim/euroc_c2_plugin/ros/ros_interface.cpp:341 on_set_stop_conditions() condition 7, invalid joint gripper
How, then should I go about setting gripper stop conditions for both the "the force exerted by the weight of the object pulling the TCP towards the floor" and "the force exerted by the gripper to hold the object in place" (According to your previous answer, "tool_force_threshold" and "joint_ext_torque_threshold", respectively)?
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