In the field of measuring techniques we are experiencing increasing demand for automation of measuring procedures due to the increasing number of measuring instruments and parameters. With automation, the required experiment can be done faster and without the need for the engineer to manually interfere with the measuring process.
In the presented document, the preparation and use of six axis manipulator is introduced. The used mechanism is required in order to test various mechanical tolerances of different magnetic encoders, where the operating position of encoder read head in relation with its magnet needs to be verified.
With known requirements for such manipulator, the chosen mechanism was provided by \emph{Standa Ltd.} manufacturer. The mechanism consists of three axis translational system, which
is responsible for setting the required position, and three axis rotational motorized system, which is needed for setting the required orientation of the end-effector. The stepper motors in each of the moving axis are controlled by four controllers, which are receiving the commands from the user software.
The modularity of the manipulator enables its assembly to many different configurations. Because of this, the kinematic model of the manipulator is not determined beforehand but is left to us to derive according to used configuration. During this process we are faced with the problem of direct kinematics, which examines the computation of external coordinates with known internal coordinate values. We also come across the reversed problem, known as the problem of inverse kinematics, where the values of external coordinates are known, and we need to compute the required values of internal coordinates. When using the manipulator, we usually send command to move the end effector to the specified target pose. From this command we need to compute the required path for each axis. Since the computed distances for each axis vary, some of the stages reach target position in shorter time than others. This behaviour can be disturbing for the user. Synchronisation of movements is introduced to remove this effect. In this procedure, we compute the parameters of trapezoidal movement profile of each axis in such a way, that all of the axis will reach the target position at the same time.
For representation of the measurement results, it is very important to determine the positional repeatability of the used mechanism. For measurement of this parameter, a standardised procedure is presented which is used to verify the required repeatability of the manipulator.
In order to provide the user with an effective way of interacting with the machine, an easy and robust user interface must be provided. We divide the program architecture to multiple layers, where all the lower layers are responsible for setting of the communication and also for the performance of complex mathematical and logical computations. Higher layers only have visibility of the functions and parameters, which are needed to be controlled by the user.
Finally, a real world measuring scenario is introduced, where manipulator is used to verify the operation of encoder with respect to various read head positions around the magnet. In the proposed program, we incrementally change the end effector position and read encoder data at each position. The acquired data enables us to verify the encoder's mechanical tolerances and also enables us to find the optimal operating position.
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