University of Twente Student Theses


Towards a ball bouncing demonstration for the T-Flex

Werff, S.J. van der (2023) Towards a ball bouncing demonstration for the T-Flex.

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Abstract:Recently, the research chair of Precision Engineering at the University of Twente has developed the T-Flex: a six degree of freedom, fully flexure-based hexapod. It has a translational workspace of 5.5 dm3, can potentially achieve accelerations up to 18 g, has a repeatability of 0.35 um RMS and has a high force sensitivity. This combination of properties is unprecedented and therefore the T-Flex is an interesting subject to display the current advancements in flexure-based mechanisms. The goal of this research is therefore to select and develop a suitable demonstration that showcases the combination of these properties. Based on a literature survey and a set of criteria, a bouncing ball demonstration is deemed most appropriate. An algorithm is developed for vertical, one-dimensional bouncing of a ball on a platform. The objective of this algorithm is to bounce a ball to a given reference height, where the platform velocity at the moment of impact can be regarded as control input to the ball. To calculate the needed platform velocity, the velocity of the ball is relevant. In previously developed ball bouncing algorithms, external sources of information are often used to reconstruct the ball state, such as cameras or force sensors. Due to the high force sensitivity of the T-Flex however, the contact force of the ball on the platform can be obtained from the torque delivered by the actuators and the inverse dynamics model of the T-Flex. The contact force is the basis for measurements as linear impulse and the time between bounces, which are the input to the developed algorithm. The algorithm for one-dimensional bouncing has also been extended to an algorithm for two-dimensional, sideways bouncing. The one-dimensional bouncing has been verified in a simulation. The two-dimensional bouncing has been simulated as well, as a proof of concept. Additionally, the one-dimensional bouncing has been experimentally tested on the T-Flex. These experiments resulted in two main observations. Firstly, the measurement of linear impulse is 31% lower than expected, the cause of which remains unknown. Secondly, it is found that air resistance is only negligible for bouncing heights lower than 0.25 m. It is therefore recommended that the measurement for the linear impulse is improved and the model for the ball trajectory is extended to account for air resistance, such that higher bouncing is possible. Although the demonstration is not yet completely functional, its feasibility is shown by comparing the required range of motion and acceleration to the properties of the T-Flex.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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