Study of the impedance control of a 6 dof robot

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Dr. Kiss Bálint
Department of Control Engineering and Information Technology

In this thesis I analyze the possibilities of impedance control of a six degree of freedom GT6A type robot in order to be possible to design and realize force and torque control methods.

I study first the applicability of the parts of the existing system. The robot is driven by a power amplifier block. For control purposes, I used two Motion Control cards made by National Instruments (one for 4 axes and one for 2 axes), which were easy to programming by the LabVIEW 2009 software.

Unfortunately, neither the robot arm nor the power amplifier block was equipped by force, torque or current sensors. Therefore we bought and installed current sensors, to measure the currents of the electric-motor. From the value of the currents, the torques of the axes can be determined. The signals of these sensors are processed by the analog-digital converter inputs of the Motion Control cards. This also made necessary the modification of the so-called wiring box, which is used to connect the power amplifier box with the Motion Control cards.

To implement the impedance control I had to determine the geometric model of the robot, the gravitational effects, and the compliance matrix. For the geometric model, I used the Denavit-Hartenberg parameters from a previous thesis [1]. For calculate the gravitational effects, the dynamic model of robot is needed, which is not available. I estimated the effects from measuring the torque of motors during a movement. Based on the symbolic equations set up to describe the gravitational forces, used an LS method for estimating the unknown parameters.

LabVIEW 2009 is used to realize the measurements and to implement the control laws and I used Matlab for the calculations involving matrices.

During the design phase, my purpose was to create a system with separated modules, to make the further developing easy.


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