Commercial and environmental demands put constant pressure on robot manufacturers to improve the efficiency of the robots they produce. Satisfying answers to efficiency questions can have a major impact on both manufacturers and users.

This thesis presents a study of energy-efficient robots with rigid links that meet the requirements of high speed and ability to work with lightweight objects at low cost. The Linköping Flywheel Robot (LFR), the prismatic variant (LFRp) of the Linköping Flywheel Robot and a spring-assisted gantry robot are described in detail and a pendulum robot is briefly mentioned.

The first part of the thesis contains an introduction to the field of high-speed robots, a problem definition and a brief introduction to the robots presented and analyzed in the thesis. The second part presents the mechanical concept of the LFR, optimizations of the concept in terms of optimal link lengths and path planning. The optimizations for the LFR focus on minimizations of maximum torque of the outer links during operation. It is shown that the maximum torque during operation can be substantially reduced. The third part of the thesis presents the mechanical concept of the spring-assisted gantry robot. The optimizations of the gantry robot focus on optimization of spring constants and minimization of motor work during operation, and it is shown that the necessary work can be considerably reduced. Four appendixes are included in the thesis: an analysis of an LFR robot with only revolute joints (Appendix A), a description of the mechanical design, the electronics and the control of a prismatic prototype variant of the LFR (LFRp) (Appendix B), an overview of the Newton-Euler equations (Appendix C) and six internationally published papers on which the thesis is built up (Appendix D). The results should be of interest in contexts such as the food industry, which typically handles lightweight objects in large volumes.