receiving 3D position of robots end effector through motive/optitrack

Hello everyone,

we are tracking the end effector position of a robot. The 3D position is captured through a camera system called Motion Capture System/ Optitrack. It recognizes the rigid body attached at the robots end effector. After capturing the position, motive sends the data to matlab and matlab saves the 3D position into a 'mat' file.

However the problem is that at random targets/ positions matlab receives (?) or saves (?) an empty array instead of an array with the 3D position. It looks for example like this:

Target1/ Position1: x, y, z

x, y, z

x, y, z

...

Target2/Position2: x, y, z

x, y, z

x, y, z

...

Target3/Position3: [ ]

Target4/Position4: x, y, z

x, y, z

x, y, z

...

Target5/Position5: [ ]

Target6/Position6: x, y, z

x, y, z

x, y, z

...

The experiments are running until the end however at some targets matlab generates the following error message:

Starting Mocap (Motion Capture) data recording...

Error while evaluating TimerFcn for timer 'timer-1'

Attempting to access the property or method of an invalid object.

Stopping Mocap (Motion Capture) data recording...

done.

This error message occurs always in the next target after I get an empty array in the previous target. For example at Target3 the array for the 3D position is empty and in the next Target (Target4) matlab generates the error message above.

Does anyone has any idea? Please help! The arrays must not be empty.