Actuators with intrinsic compliant elements are more and more being adopted in the biorobotics world. However, they also have a number of unfavorable characteristics such as bulkiness and a relatively high design complexity. Meanwhile, rigid actuators that are generally more compact and simple to implement are attractive for a number of applications. Yet, their inherent limitations in achieving a particular compliance characteristic might be in conflict with other biorobots design requirements. In this paper, we present experimental results to obtain more insights about the trade-offs in using three different types of single degree-of-freedom joint actuators, namely a geared rigid motor, a direct driven rigid motor and a variable stiffness actuator for biorobotic applications. Various aspects such as impact force behavior, stiffness range and manipulability as well as power consumption of the three actuator types are further investigated and compared in this paper.
A bstract -A magnetostat i c analyt i cal model i s created to analyze and design a small-s i zed magnet i c gear for a robot i c appl i cat i on. Through a parameter var i at i on study, i t i s found that the i nner rotor magnet height i s h i ghly i ntluent i al to the torque, and based on wh i ch, the design i s performed. Several magnet i c gears w i th d i fferent rotor pole pa i r comb i nat i ons are designed to suffice the required gear ratio, taking into account manufactur i ng constra i nts of such a small dev i ce. A des i gn i s chosen to be manufactured consider i ng the following criteria: mater i al cost, cogg i ng torque level and rotat i onal st i ffness. Measurement and 3D FEM s i mulat i on results indicate that discrepanc i es between the expected and measured torque as well as effic i ency ar i se due to ax i al tlux leakage, wh i ch becomes severe i n the presence of bear i ngs. Meanwh i le, a frequency response measurement result shows that the first resonant mode i n the magnet i c gear, wh i ch has i mpl i cat i ons on control, can be well est i mated given the s i mulated values of rotat i onal st i ffness, damp i ng, and rotor i nert i a and thus could actually be ant i c i pated early i n the design phase.
This paper presents the modeling and design of an actuator consisting of an electrical motor and a magnetic gear. To minimize the overall actuator dimensions, both of the electromagnetic devices need to be optimally designed and matched. An issue in performing a simultaneous design as such arises from a high number of design variables that significantly increases the complexity of the optimization problem. A method to reduce the design variables is discussed in this paper, which is the application of response surface methodology (RSM) to represent the optimized torques of the electrical motor and magnetic gear as polynomial functions of their respective dimensions. Prior to the application of RSM, optimization problem statements are defined for the electrical motor and magnetic gear, for which the optimization objective and constraint functions are derived from analytical electromagnetic models of the considered electromagnetic devices.
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