**Preface to "Kinematics and Robot Design II (KaRD2019) and III (KaRD2020)"**

The Special Issue series on "Kinematics and Robot Design" (KaRD series) is hosted by the open access journal Robotics. KARD series started in 2018 and is now an open environment where researchers can present their studies and discuss all topics focused on the many aspects that involve kinematics in the design of robotic/automatic systems by using also supplementary multi-media materials uploaded during submission. Even though KaRD series publishes one Special Issue per year, all received papers are peer-reviewed as soon as they are submitted, and, if accepted, they are immediately published in Robotics and appear on the website of the KaRD issue. The open access nature of this series allows authors to easily share their papers and accompanying supplementary materials with the reference scientific community on many platforms where they can receive comments from other researchers. Furthermore, upon submission, authors can publish their preprint online at https://www.preprints.org/ for receiving comments to consider together with reviewer remarks when preparing revised versions of their papers. In short, the KaRD series is an "agora" where researchers meet with one another and efficiently exchange their experiences. These characteristics distinguish the KaRD series from numerous serial conferences/publications related to mechanisms and robotics.

KaRD2019 (https://www.mdpi.com/journal/robotics/special issues/KRD2019) and KaRD2020 (https://www.mdpi.com/journal/robotics/special issues/KaRD2020) are the second and third issues of the KaRD series. Beginning with KaRD2020, the activity of the Guest Editor has been supervised/supported by a scientific committee, as it is the case in all well-established serial international conferences/publications. The committee comprises the following members whose service is gratefully acknowledged: Massimo Callegari (Polytechnic University of Marche, Italy); Juan Antonio Carretero (University of New Brunswick, Canada), Yan Chen (Tianjin University; China), Daniel Condurache ("Gheorghe Asachi" Technical University of Ias, i, Romania); Xilun Ding (Beijing University of Aeronautics & Astronautics, China); Mary Frecker (Penn State—College of Engineering, USA); Clement Gosselin (Laval University, Canada); Just Herder (TU Deft, Netherlands); Larry Howell (Brigham Young University, USA); Xianwen Kong (Heriot-Watt University, UK); Pierre Larochelle (South Dakota School of Mines & Technology, USA); Giovanni Legnani (University of Brescia, Italy); Haitao Liu (Tianjin University, China); Daniel Martins (Universidade Federal de Santa Catarina, Brazil); Andreas Mueller (Johannes Kepler Universitat, Austria); Andrew ¨ Murray (University of Dayton, USA), Leila Notash (Queen's University, Canada); Matteo Palpacelli (Polytechnic University of Marche, Italy); Alba Perez (Remy Robotics, Barcelona, Spain); Victor Petuya (University of the Basque Country, Spain), Jose Maria Rico Martinez (Universidad de ´ Guanajuato, Mexico); Nina Robson (California State University, Fullerton, USA); Jon M. Selig (London South Bank University, UK); Bruno Siciliano (University of Naples Federico II, Italy); Tao Sun (Tianjin University, China), Yukio Takeda (Tokyo Institute of Technology, Japan); Federico Thomas (Institute of Industrial Robotics, Spain); Volkert Van Der Wijk (TU Deft, Netherlands).

KaRD2019, together with KaRD2020, received 22 papers and, after the peer-review process, accepted only 17 papers. This volume collects 17 accepted papers and is organized as follows. The first six papers [1–6] investigate or review the kinematics of parallel/serial manipulators from a theoretical point of view. Then, the successive four papers [7–10] address medical robotics issues; two papers [11, 12] that follow deal with performance analyses. Finally, paper [13] deals with education in robotics, and the last four papers [14–17] deal with robot design.

[1] Ruggiu, M.; Muller, A. Investigation of Cyclicity of Kinematic Resolution Methods for Serial and ¨ Parallel Planar Manipulators. Robotics 2021, 10(1), 9. doi: 10.3390/robotics10010009.

[2] Shen, H.; Xu, Q.; Li, J.; Yang, T. The Effect of the Optimization Selection of Position Analysis Route on the Forward Position Solutions of Parallel Mechanisms. Robotics 2020, 9(4), 93. doi: 10.3390/robotics9040093.

[3] Di Gregorio, R. A Review of the Literature on the Lower-Mobility Parallel Manipulators of 3-UPU or 3-URU Type. Robotics 2020, 9(1), 5. doi: 10.3390/robotics9010005.

[4] Ruggiu, M.; Kong, X. Reconfiguration Analysis of a 3-DOF Parallel Mechanism. Robotics 2019, 8(3), 66. doi: 10.3390/robotics8030066.

[5] Schappler, M.; Tappe, S.; Ortmaier, T. Modeling Parallel Robot Kinematics for 3T2R and 3T3R Tasks Using Reciprocal Sets of Euler Angles. Robotics 2019, 8(3), 68. doi: 10.3390/robotics8030068.

[6] Huber, G.; Wollherr, D. Efficient Closed-Form Task Space Manipulability for a 7-DOF Serial Robot. Robotics 2019, 8(4), 98. doi: 10.3390/robotics8040098.

[7] Oka, T.; Solis, J.; Lindborg, A.; Matsuura, D.; Sugahara, Y.; Takeda, Y. Kineto-Elasto-Static Design of Underactuated Chopstick-Type Gripper Mechanism for Meal-Assistance Robot. Robotics 2020, 9(3), 50. doi: 10.3390/robotics9030050.

[8] Yamine, J.; Prini, A.; Nicora, M.; Dinon, T.; Giberti, H.; Malosio, M. A Planar Parallel Device for Neurorehabilitation. Robotics 2020, 9(4), 104. doi: 10.3390/robotics9040104.

[9] Filippeschi, A.; Griffa, P.; Avizzano, C. Kinematic Optimization for the Design of a Collaborative Robot End-Effector for Tele-Echography. Robotics 2021, 10(1), 8. doi: 10.3390/robotics10010008.

[10] Castelli, K.; Carnevale, M.; Giberti, H. Development of an Automatic Robotic Procedure for Machining of Skull Prosthesis. Robotics 2020, 9(4), 108. doi: 10.3390/robotics9040108.

[11] Bussola, R.; Legnani, G.; Callegari, M.; Palmieri, G.; Palpacelli, M. Simulation Assessment of the Performance of a Redundant SCARA. Robotics 2019, 8(2), 45. doi: 10.3390/robotics8020045.

[12] Schulz, S. Performance Evaluation of a Sensor Concept for Solving the Direct Kinematics Problem of General Planar 3-RPR Parallel Mechanisms by Using Solely the Linear Actuators' Orientations. Robotics 2019, 8(3), 72. doi: 10.3390/robotics8030072.

[13] Castelli, K.; Giberti, H. Additive Manufacturing as an Essential Element in the Teaching of Robotics. Robotics 2019, 8(3), 73. doi: 10.3390/robotics8030073.

[14] Di Gregorio, R. A Novel 3-URU Architecture with Actuators on the Base: Kinematics and Singularity Analysis. Robotics 2020, 9(3), 60. doi: 10.3390/robotics9030060.

[15] Palpacelli, M.; Carbonari, L.; Palmieri, G.; D'Anca, F.; Landini, E.; Giorgi, G. Functional Design of a 6-DOF Platform for Micro-Positioning. Robotics 2020, 9(4), 99. doi: 10.3390/robotics9040099.

[16] Achilli, G.; Valigi, M.; Salvietti, G.; Malvezzi, M. Design of Soft Grippers with Modular Actuated Embedded Constraints. Robotics 2020, 9(4), 105. doi: 10.3390/robotics9040105.

[17] Castelli, K.; Zaki, A.; Dmytriyev, Y.; Carnevale, M.; Giberti, H. A Feasibility Study of a Robotic Approach for the Gluing Process in the Footwear Industry. Robotics 2021, 10(1), 6. doi: 10.3390/robotics10010006.

> **Raffaele Di Gregorio** *Editor*
