University of Twente Student Theses


Design of an anti-slip control system of a Segway RMP 50 omni platform

Lieftink, R.J. (2017) Design of an anti-slip control system of a Segway RMP 50 omni platform.

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Abstract:In the i-Botics centre, founded by TNO and the University of Twente, a project is carried out focused on telerobotics. With telerobotics a robot is able to perform tasks on remote locations. For some of these tasks human expertise is needed for assessing and responding to unpredictable situations. To performthese tasks to usermust be able to exactly feel what the robot is doing. With the use of sensors and haptic feedback this can be made possible. The robot used consists out of a KUKA Light-Weight Robot 4+ with a RightHand Robotics ReFlex TakkTile attached to a platform. This platform can move omni directional using the Segway RMP 50 omni, of which the velocity is controlled by a joystick. The drawback of this system is that omnidirectional wheels can slip on smooth surfaces. This results in a deviation from the desired motion. The goal of this thesis is to build a system that corrects unwanted motion using sensors and feedback control. The Segway RMP 50 omni is a platformwhich canmove omni directional, due to the rotated forces which act upon the rollers of the mecanum wheels. The slip which occurs in these mecanum wheels is the consequence of a higher contact force than friction force. This slip creates a deviation from the desired direction. A slip ratio can be calculated based on theoretical wheel velocity and the actual velocity of the wheel. The open loop system which does not take the slip in consideration is changed into a closed loop system. Different approaches of a closed loop system to cancel out the slip have been looked at. The slip controller using velocity adjustment will be used. The slip must be detected with an internal sensor as a reference point in combination with the encoders of the Segway, the extra sensor added is the IMU. The slip controller will determine the slip ratio by using the IMU measurement and the encoder measurement. Based on the calculated slip ratio the velocity scaling is determined. Due to the noise, this scaling is filtered with a moving average filter for a smooth controller. Scaling this velocity results in a lower contact force, which reduces the slip. The controller showed that the slip was detected by reducing its velocity. Due to this scaling the deviation of the platformwas lower. The tests that are donewere the two extremes. One surface with a high friction surface and one with a low friction surface. The high friction surface showed that both controllers worked properly, but still had a higher deviation than required due to the weight distribution. The low friction surface showed that the combination of the University floor and the wheels can not be solved, because the friction between the two is to low. Due to this low friction the minimum speed and maximum deviation was not made and the system started oscillating. These two extreme test conditions made it hard to compare the results. It is recommended to use other wheels, which can exert more friction on the ground. Also different test conditions can be recommended, to get a better results for the comparison between the open loop and closed loop system. Robotics
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:52 mechanical engineering, 53 electrotechnology
Programme:Electrical Engineering BSc (56953)
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