Igor Gaponov

Twisted String Actuation Systems: A Study of the Mathematical Model and a Comparison of Twisted Strings

This paper presents an improved mathematical model of a twisted string transmission system. The proposed mathematical model has been validated experimentally and provided a better match with the practical data in comparison with the conventional model. Translational transmission systems based on twisted strings coupled with electric motors can compose light-weight, compact, and mechanically simple actuators that can be used in various robotic applications. An extensive experimental study on the performance of different types of strings during twisting is presented. The drawbacks and advantages of each type of strings, along with some of their properties, are discussed.

Towards variable stiffness control of antagonistic twisted string actuators

This paper shows the possibility of using two antagonistic twisted strings actuators as a new type of variable stiffness actuator. Variable stiffness model of the twisted string actuator is identified empirically, and the control strategy is proposed for simultaneous position and stiffness control of the actuator. A variable stiffness linear joint actuated by antagonistic twisted string actuators is proposed as a target system. The proposed model and control strategy make it possible to control the position and the stiffness of the joint without position and force sensor at the load side. The developed variable stiffness linear joint can be effectively used in applications where weight distribution is vital, such as exoskeleton systems and low weight manipulators.

Bidirectional elbow exoskeleton based on twisted-string actuators

In this paper, a bidirectional elbow exoskeleton device based on rotational twisted string actuators is proposed. A novel actuation mechanism incorporating antagonistic motors is proposed and its kinematic model is presented along with its experimental evaluation. Two antagonistic actuation mechanisms provide the motion of the forearm link in both directions thus allowing to position the forearm precisely even in the presence of such disturbances as friction, external forces, and at different positions of the upper arm link. In addition, we propose a method to control the antagonistic exoskeleton based on the actuators kinematics. The developed twisted strings-driven elbow exoskeleton can be effectively used in a variety of haptics, teleoperation, and rehabilitation applications.

A study on twisted string actuation systems: Mathematical model and its experimental evaluation

This paper presents an improved mathematical model of a single twisted string transmission system. The proposed mathematical model has been validated experimentally and provided a better match with the practical data in comparison to the conventional model. Translational transmission systems based on twisted strings coupled with electrical motors can compose light-weight, compact, and mechanically simple actuators which can be used in various robotic applications. Hands-on instructions on design of twisted string transmission systems presented in this paper are intended to help engineers in development of such actuation systems.

Quadcopter design and implementation as a multidisciplinary engineering course

This paper describes a sample syllabus for the undergraduate course whose main objective is the design and implementation of quadrotor helicopter system. The class is intended to provide the students with both theoretical and practical knowledge in the areas of mechanical engineering and design, system integration, hardware programming, and control system design and implementation. The class has the objectives which are very clear for the students, and gaining practical skills in such a blend of several unrelated technical fields at the same time can give the students unique experience of system design and integration, which can prove to be very useful in their future career.

A preliminary study on a twisted strings-based elbow exoskeleton

This paper presents a new concept of a 1-DOF elbow exoskeleton driven by a twisted strings-based actuator. A novel joint actuation mechanism is proposed and its kinematic model is presented along with its experimental evaluation, and guidelines on how to choose the strings suitable for such an exoskeleton are given. We also proposed and experimentally verified a human intention detection method which takes advantage of intrinsic compliance of the mechanism. The study showed that the developed twisted strings-driven elbow exoskeleton is light, compact and have a high payload-to-weight ratio, which suggests that the device can be effectively used in a variety of haptics, teleoperation, and rehabilitation applications.

Telerobotic system for cell manipulation

In this paper, telerobotic system for cell injection applications is proposed. Fidelity and stability are contradicting factors in teleoperation. Most of cells manipulations nowadays are performed manually by the human operators. These highly precise operations require high-skilled professional operators. However, the success and survival rate of the cells is very low due to the great sensitivity of cells. Moreover, while manipulating, operator cannot feel any interaction with the cells because of their negligible mass, therefore all the operations are based on the visual information provided by the high-precision microscope. In addition, during every operation the humanpsilas hand has a certain vibration that can affect the quality of teleoperation, especially in telesurgery, nanomanipuation and other precise tasks. All of the reasons listed above show that the cells manipulation is an exclusively complex task for a human operator to perform. Therefore, applying telerobotic system for the cells manipulation may provide us with many advantages and could help us to overcome the problems listed above.

Passively adjustable gear based on twisted string actuator: Concept, model and evaluation

Actuators with adjustable transmission ratios are required in a variety of robotics and automation applications, spanning from human assistive devices and mobile robots to general manipulators. Most existing self-adjustable actuators are bulky and mechanically complex, which often makes their implementation challenging. In this work, we propose a novel passively-adjustable transmission mechanism based on a twisted string actuator. Twisted string actuator is a light, cheap, and mechanically simple actuator, in which twisted strings contract as a result of twisting and therefore act as a translational gear. If one introduces a physical offset between the twisted strings, this changes a ratio between the speed and output force provided by actuator. This work introduces a kinematical model of such actuator for the configuration when a physical offset between the strings is present. In order to experimentally verify the proposed mathematical model, we designed and manufactured a twisted string actuator with variable offsets between the strings. Additionally, in this paper we also propose an idea for passively adjustable gear, controlled by twisted string actuator according to the proposed kinematical model. The main advantages of the proposed passively adjustable gear are its light weight, compliancy and mechanical simplicity, which make it attractive for implementaion in various areas of haptics, teleoperation, wearable and lightweight robotics.

Rotational twisted string actuator with linearized output: Mathematical model and experimental evaluation

Twisted string actuator is a compliant, light, and mechanically simple module. The actuation principle is based on the contraction of the strings, where a low torque - high speed dc motor is capable of providing high forces. Such actuators are very light, quiet, compliant, mechanically simple and provide a possibility to move motors away from the actu- ating joint. Implementation of these actuators can drastically decrease the weight and size of certain robotic systems such as exoskeletons, manipulators and humanoid robots. However, these actuators have disadvantages such nonlinear transmission ratio, which is found as a ratio between the angle of twisting of the strings and their resulting contraction. In this paper, we propose a linearized output transmission mechanism with rotational motion as an output which incorporates a twisted string actuator. The designed mechanism allows to linearize the relationships between the input and output displacements and forces. The proposed design has been validated theoretically and evaluated through a series of experiments and simulations. A detailed analysis of the performance of the proposed mechanism is presented in this paper.

Study on a Two-Staged Control of a Lower-Limb Exoskeleton Performing Standing-Up Motion from a Chair

The paper is concerned with control over a lower-limb exoskeleton device when it performs a sit-to-stand motion from a chair. A mathematical model describing full dynamics of the device is derived, and the strategies to facilitate the desired motion are outlined. A control system based on a modified Jacobian transpose is proposed, and its performance is evaluated in a series of numerical experiments. The simulations proved that the proposed control method can be successfully used to provide stable sit-to-stand motion from a chair.