Abstract
M.Tech. (Electrical Engineering)
The challenges faced by modern industrial robots and robots in general are increasing in cornplexity. A modern robot can be defined as a technological system. capable of replacing or assisting man in carrying out a variety of physical tasks. Thus the implementation of advanced technology in the field of industrial robotics poses different challenges to those faced by engineers in other fields. The reason for this lies mainly in the fact that robots have to be be able to
interact with their environment in some intelligent way. For the robot to be able to accomplish this. it must be able to obtain information about its immediate surroundings. and/or its position in the surroundings. In the case of industrial or other stationary robots. the knowledge about its surroundings are of less importance than its own position and the position of the relevant workpieces in the work space.
Traditionally the position of a robot arm is measured using position encoders mounted at the
joints of the robot arm. The combination of information obtained from these sensors gives the position of the endpoint of the arm. To ensure that the encoder positions accurately reflect the actual position of the arm. the arms have to be rigid, resulting in a heavy. bulky and costly system. If it were possible to determine the endpoint of a robot arm without using the
joints of the arm as reference points, it would be possible to design more flexible robot arms.
resulting in less costly and more maneuverable systems. Various solutions were considered
for this measurement problem and from these it was decided to investigate the use of inertial
measurement technology to determine the endpoint position of a flexible robot arm.
To test the use of gyroscopes as feedback sensors in the position control of a flexible robot arm.
a small low cost robot arm was developed. The design was based on an articulated robot arm
with three degrees of freedom (DOF). The system was designed to be fitted with a flexible arm
segment to evaluate the gyroscope-based feedback system. The system was further fitted with
traditional position sensors to be used as the benchmark against which the gyroscope-based
control system was to be compared. Making use of the traditional position sensors the endpoint
of the arm can be accurately placed in a space of :3mm x 4mm x 1mni. When the robot was fitted
with the flexible arm segment the gyroscopes were able to measure movement of the flexible ann.
which the traditional sensors could not detect.
Using the gyroscopes as position feedback. the robot was able to track the potentiometer position
within 0.19° under dynamic conditions, but under stationary conditions. the error was 6.50
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Based on the results obtained. it was concluded that the displacement of a robot arm segment
can be determined using inertial measurement technology. The low cost sensors used proved
the concept. but for reliable operation. higher accuracy sensors would be required aided with
information obtained from other sensors. i.e, potentiometers resolvers or other absolute encoders.