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An enquiry into the relation between components and their composition on desired performance and cost of pick&place robotic arms

Schurink, T. (2016) An enquiry into the relation between components and their composition on desired performance and cost of pick&place robotic arms.

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Abstract:The purpose of this paper is making a model to relate desired performances to required components, their composition and their cost so it will become possible to design and produce high quality robotic arms at the right cost. To make this relation, it is vital to first understand the concepts of the performances speed, power, accuracy and precision. Speed in the case of electric motors is often rotational speed. Torque is used as a measure of how strong a motor is, defined by how much force it can deliver over an arm. Accuracy is how close the average of multiple shots are to the centre of a target, and precision is how close these shots are grouped together. The main components of a robotic arm are the motors, bearings and frame, together with other supporting components they make up the arm. The selection of these components are all based on the performance required by the user. The electro motors typically used in household to professional arms are servos and stepper motors, both with different operating mechanics and electronics. Servos typically deliver more torque, can run at higher speeds, have internal position feedback, can have an external feedback loop and are generally more expensive. Stepper motors work at low speeds, can be fitted with a gearbox to increase torque, do not have a internal position feedback and are generally cheaper than servos. This paper will present a formula to calculate the required torque of a motor, and to calculate the resulting resolution of the motor. There is a large variety of bearings, but the ones most frequently used in robotic arms are deep groove ball bearings and angular contact bearings. When moderate loads are presented both axial and radial, for example at the rotating base of the arm, or in the arm itself when dealing with high inertia, angular contact bearings are well suited. When mostly radial loads are applied, for example in the arm dealing with low inertia loads, deep groove ball bearings are most beneficial. Internal radial clearance ensures smooth and consistent operation of bearing but leads to imprecision in the system, which can be calculated using the bore and outer diameter of the bearing, multiplied by the length of the arm. When the frame of the robotic arm is subjected to high forces perpendicular to the arm, it is advised to make the arm out of tubular material. When however the arm is mostly subjected to light lifting loads, sheet metal results in the best strength to weight ratio. Topolgical optimalization software is recommended to increase this ratio. Other modelling or FEM software can be used to calculate the displacement under load on the arm. A prototype was made based on the information presented in this paper to validate the models made in this paper. The model for sizing the motor turned out to be accurate. The model for estimating the precision of the endeffector is mostly correct but did not take into account any inaccuracies caused by manufacturing.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:20 art studies
Programme:Industrial Design BSc (56955)
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