3D printing and particularly fused filament fabrication is widely used for prototyping and fabricating low-cost customized parts. However, current fused filament fabrication 3D printers have limited nozzle condition monitoring techniques to minimize nozzle clogging errors. Nozzle clogging is one of the most significant process errors in current fused filament fabrication 3D printers, and

Purpose-Fused deposition modelling (FDM) is one of the most popular additive manufacturing (AM) processes, and is widely used for prototyping and fabricating low cost customised parts. Current FDM machines have limited techniques to monitor process conditions in order to minimise process errors, such as nozzle clogging. Nozzle clogging is one of the most significant process errors in current FDM machines, and may cause serious consequences such as print failure. This paper presents a physics-based dynamic model suitable for monitoring nozzle clogging in FDM machines. Design/Methodology/Approach-Liquefier mount of FDM extruder is analysed as a beam excited by a uniform loading distributed over a partial length. Boundary conditions and applied loads for direct type FDM extruder are identified and discussed. Simulation of nozzle clogging was performed by using nozzles of different diameter from 0.5 mm to 0.2 mm, in step change of 0.1 mm. Sets of experiments were carried out by measuring vibrations of the liquefier block mount during FDM extrusion. Findings-The mount of a liquefier block in FDM extruder can be used to place a vibration sensor in order to monitor process errors such as nozzle clogging. Liquefier block mount's transverse vibration amplitudes increase non-linearly when nozzle starts to block. Practical implications-The proposed model can be effectively used for monitoring nozzle clogging in FDM machines, as it is based on the physics relating the FDM process parameters and the nozzle blockage. Originality/value-The novelty of this paper is the unique method of modelling the FDM process dynamics that can be used for monitoring nozzle clogging.

Robotics research and education have gained significant attention in recent years due to increased development and commercial deployment of industrial and service robots. A majority of researchers working on robot grasping and object manipulation tend to utilize commercially available robotmanipulators equipped with various end effectors for experimental studies. However, commercially available robotic grippers are often expensive and are not easy to modify for specific purposes. To extend the choice of robotic end effectors freely available to researchers and educators, we present an open-source lowcost three-finger robotic gripper platform for research and educational purposes. The 3-D design model of the gripper is presented and manufactured with a minimal number of 3-D-printed components and an off-the-shelf servo actuator. An underactuated finger and gear train mechanism, with an overall gripper assembly design, are described in detail, followed by illustrations and a discussion of the gripper grasping performance and possible gripper platform modifications. The presented open-source gripper platform computer-aided design model is released for downloading on the authors research lab website (www.alaris.kz) and can be utilized by robotics researchers and educators as a design platform to build their own robotic end effector solutions for research and educational purposes. INDEX TERMSOpen-source robotic gripper, gear train mechanism, 3D printing, underactuation, adaptive grasping. 638 2169-3536

In this paper authors present an open source lowcost basic robotic end effector platform for facilitating research on robotic grasping. The 3D design model of a three fingered underactuated robotic gripper is presented and manufactured with minimal number of 3D printed components and an off-theshelf servomotor actuator. An underactuated finger, gear train mechanisms and an overall gripper assembly design are described in details followed by illustration and discussion of grasping of objects with various geometries. The presented open source gripper design will be released for downloading on the authors' research lab web-site www.alaris.kz and can be useful for robotic researchers as a platform to build their own robotic end effector solutions for research and educational purposes.