ROS moveit constraints - c++

Question

I’m trying to use move it to move an arm vertically ONLY. The idea is to keep the tip of the end-effector to always keep the x and y-axis position and change the z-axis position in each iteration, keeping its orientation as well. I also want to constrain the movement from start-position to end-position in each iteration to follow this constraints (x and y fixed, z changing only). I don’t care about how much the joints change as long as the gripper (my end-effector) only moves upwards.
I tried to do it as presented bellow, but i don’t see any constraints being followed? What am I doing wrong?
int main(int argc, char **argv){
ros::init(argc, argv, "move_group_interface_tutorial");
ros::NodeHandle node_handle;
ros::AsyncSpinner spinner(1);
spinner.start();
/* This sleep is ONLY to allow Rviz to come up */
sleep(20.0);
moveit::planning_interface::MoveGroup group_r("right_arm");
robot_state::RobotState start_state(*group_r.getCurrentState());
geometry_msgs::Pose start_pose;
start_pose.orientation.x = group_r.getCurrentPose().pose.orientation.x;
start_pose.orientation.y = group_r.getCurrentPose().pose.orientation.y;
start_pose.orientation.z = group_r.getCurrentPose().pose.orientation.z;
start_pose.orientation.w = group_r.getCurrentPose().pose.orientation.w;
start_pose.position.x = group_r.getCurrentPose().pose.position.x;
start_pose.position.y = group_r.getCurrentPose().pose.position.y;
start_pose.position.z = group_r.getCurrentPose().pose.position.z;
//const robot_state::JointModelGroup *joint_model_group = start_state.getJointModelGroup(group_r.getName());
//start_state.setFromIK(joint_model_group, start_pose);
group_r.setStartState(start_state);
moveit_msgs::OrientationConstraint ocm;
ocm.link_name = "r_wrist_roll_link";
ocm.header.frame_id = "base_link";
ocm.orientation.w = 0.0;
ocm.absolute_x_axis_tolerance = 0.0;
ocm.absolute_y_axis_tolerance = 0.0;
ocm.absolute_z_axis_tolerance = 0.1;
ocm.weight = 1.0;
moveit_msgs::Constraints test_constraints;
test_constraints.orientation_constraints.push_back(ocm);
group_r.setPathConstraints(test_constraints);
geometry_msgs::Pose next_pose = start_pose;
while(1){
std::vector<geometry_msgs::Pose> waypoints;
next_pose.position.z -= 0.03;
waypoints.push_back(next_pose); // up and out
moveit_msgs::RobotTrajectory trajectory;
double fraction = group_r.computeCartesianPath(waypoints, 0.005, 0.0, trajectory);
/* Sleep to give Rviz time to visualize the plan. */
sleep(5.0);
}
}

Answer 1

I believe that the problem is this one:
ocm.orientation.w = 0.0;
If you look at moveit_msgs::OrientationConstraint reference you find the interpretation of that orientation field.
# The desired orientation of the robot link specified as a quaternion
geometry_msgs/Quaternion orientation
However you are setting all the fields of the quaternion to 0 (imaginary x,y and z are initialized with 0 if not specified) which could cause unexpected behaviour.
If you've followed this tutorial, you could have seen that the author set ocm.orientation.w = 1.0; which means no change in orientation (i.e. roll pitch and yaw angles are equal to 0). Thus, try to specify a realistic orientation for your constraint.
Last but not least, for the sake of clearness it could be better to write concisely the start_pose initialization:
geometry_msgs::Pose start_pose = group_r.getCurrentPose().pose;