Abstract ▼ AI-Helper

The work describes an actuator based on linear contraction of nonstretchable strings due to their twisting. The idea of twisting a rope in order to increase output force was used by ancient people in various building construction and military applications. These days, researchers use such approach i...

The work describes an actuator based on linear contraction of nonstretchable strings due to their twisting. The idea of twisting a rope in order to increase output force was used by ancient people in various building construction and military applications. These days, researchers use such approach in order to create light, compliant, silent and powerful actuators, in which a string connected to an electric motor acts as a gear.
When a load is attached to the string on the other end, the rotation imposed on the string by the motor will reduce the length of the string, thus causing the translational motion of the load due to the generated pulling force. Such actuators can transfer power over distance; they are compliant, back drivable and light, which can be beneficial for exoskeleton systems, mobile and surgical robots and other robotic systems.
In this work we improved the performance of twisted string actuators, by developing more accurate mathematical model, studying various characteristics and operating conditions of it and by proposing and developing robotic applications driven by it.
The proposed mathematical model in this work improves the accuracy of twisted string actuators and explains the nature of strings behavior while twisting. The proposed model allows to control such actuators without any force or displacement sensors. Also the previously proposed models had an important issue of insensitivity for the change of applied work load. This issue is addressed in the work.
An extensive experimental study on the performance of different types of strings during twisting is presented, where the string with the best performance is chosen. The drawbacks and advantages of twisted string actuators along with detailed studies on its characteristics are presented.
The step by step guideline is designed in order to help engineers and researchers to develop robotic systems based on twisted string actuator.
The linear and rotational type of actuators based on twisted string principle are proposed and evaluated in this work. Both are supported with mathematical models, which were evaluated experimentally.
Variable stiffness elbow exoskeleton based on rotational twisted string actuator was developed. The use of twisted string actuator allowed us to create compliant, powerful system that can be actuated by operator without a use of any force sensors. The control algorithm and evaluation of prosed exoskeleton is presented.
Finally, a variable stiffness control of antagonistic twisted string actuators was proposed and evaluated. A variable stiffness linear joint was designed and tested, where its position and stiffness can be controlled simultaneously without a use of force or position sensors at the load side.
The paper contains six chapters with conclusion and bibliography.