Tomi Ylikorpi

A Novel Marsupial Robot Society: Towards Long-Term Autonomy

Within this paper a novel marsupial multi-robot system intended for long-term operation, the Marsubot Society, is introduced. The Marsubot Society is a platform for robotics and multi-robot system algorithm development. In a system that needs to operate autonomously for extended periods of time, energy is of the essence. The challenges that lie in the energy economy are how to distribute and access energy and what the system can do with the resources. The multi-robot system’s capabilities and limitations are discussed. Results of preliminary tests are presented and ideas for future work introduced.

Novel design of biped robot based on Linear Induction Motors

This work reports the preliminary results on a new design concept for bipedal walking robots. The concept is based on the actuators (linear induction motors), and the prospect that these actuators provide to combine passive dynamic walking with active walking. Comprehensive mechanical and dynamic simulations were done to decide the suitable parameter for the actuators and the mechanical design. This paper presents results from the early stages of the actuators simulations until the preliminary result on equilibrium control tested in the real robot. These results show promising outcome on the use of these actuators for more complex equilibrium control and walking algorithms. The energy consumption is a key factor for further consideration of this actuators and design approach.

Dynamic modeling and obstacle-crossing capability of flexible pendulum-driven ball-shaped robots

Abstract Ball-shaped robots present a novel and widely studied approach for mobile robotics. Despite the essential benefit of the ball-robot that it cannot flip over or fall down, the robot’s physical construction often severely limits the ball mobility in uneven terrain. The customarily applied quasi-static motion model makes the anticipated theoretical robot mobility even worse, because it completely ignores ball dynamics and therefore seriously under-estimates the robot’s obstacle-crossing capability. The energy-based model, sometimes applied instead of the quasi-static model, over-estimates ball mobility and becomes inconvenient when an active driving motor is added to the system. This paper introduces a new extended dynamic model for flexible pendulum-driven ball-shaped robots, as well as a simulation-based method to predict the robot’s step-crossing capability. The extended dynamic model allows rolling, bouncing and slipping of the robot, and it includes a simplified contact model for the ball-obstacle-interaction. The simulation results have been compared to experimental results obtained with a physical robot. The comparison shows that the new dynamic model and contact model outperform the traditionally applied quasi-static and energy-based models. The new dynamic model may be applied in mobility analysis of ball-robot designs, for path planning, as well as for control algorithm development.

Unified Representation of Decoupled Dynamic Models for Pendulum-Driven Ball-Shaped Robots

Dynamic models describing the ball-robot motion form the basis for developments in ball-robot mechanics and motion control systems. For this paper, we have conducted a literature review of decoupled forwardmotion models for pendulum-driven ball-shaped robots. The existing models in the literature apply several different conventions in system definition and parameter notation. Even if describing the same mechanical system, the diversity in conventions leads into dynamic models with different forms. As a result, it is difficult to compare, reproduce and apply the models available in the literature. Based on the literature review, we reformulate all common variations of decoupled dynamic forward-motion models using a unified notation and formulation. We have verified all reformulated models through simulations, and present the simulation results for a selected model. In addition, we demonstrate the different system behavior resulting from different ways to apply the pendulum reaction torque, a variation that can be found in the literature. For anyone working with the ball-robots, the unified compilation of the reformulated dynamic models provides an easy access to the models, as well as to the related work.

Dynamic Obstacle Overcoming Capability of Pendulum-driven Ball-Shaped Robots

This paper discusses dynamic step-crossing capability of pendulum-driven ball-shaped robots. We introduce an extended dynamic model that allows modeling of ballrobot rolling, bouncing and slipping. Based on the new model, our simulations predict the maximum over-passable step-height for the robot. The simulation results agree well with the result from a parallel simulation in Adamssoftware as well as with practical experiments. The new dynamic model can be applied for mobility analysis of robot-ball designs as well as for path planning.

Assessment of limit-cycle-based control on 2D kneed biped

This work presents an assessment of different control techniques based on Limit Cycle Walking. The study is performed on a two-dimensional kneed bipedal simulator developed with Open Dynamics Engine, which includes realistic configuration of weight allocation, link length, inertia distribution and impacts. The controllers are model-based driven from an analytic 2D kneed biped. Several controllers from the Computed Torque (CT) family together with a Passivity Based controller (PBC) are compared based on their energy efficiency and robustness. The previous controllers are used in their original form, with minor adjustment to handle hybrid systems such as the kneed biped case. PBC proved not suitable for real implementation however a combined strategy between PBC and a soft PD control has shown promising results. PD Computed Torque control also offered high tolerance to disturbances with reasonable energy consumption. Furthermore, the performance of all the controllers showed high dependency on the parameters of the robot.

Idle state stability, limit cycle walking & regenerative walking: Towards long time autonomy in bipeds

This work presents an integral approach to tackle energy issues in bipedal robots. It introduces three combined ideas to increase these robots’ autonomy: First, the exploitation of the inherent equilibrium that should exist in the rest position of a welldesigned mechanism; then, the efficient usage of the energy to walk based on the natural limit cycle of the system; and finally, the harvest of energy based on the new idea of regenerative walking. Simulations and experimental tests show promising results of this approach, built under a delicate equilibrium between appropriate control scheme, suitable mechanical design and proper actuators choice.

Gyroscopic Precession In Motion Modelling Of Ball-Shaped Robots

This study discusses kinematic and dynamic precession models for a rolling ball with a finite contact area and a point contact respectively. In literature, both conventions have been applied. In this paper, we discuss in detail the kinematic and dynamic models to describe the ball precession and the radius of a circular rolling path. The kinematic model can be used if the contact area and friction coefficient are sufficient to prevent slippage. The dynamic precession model has significance in multi-body simulation environments handling rolling balls with ideal point contacts. We have applied both the kinematic and dynamic precession model to evaluate the no-slip condition of the existing GimBall-robot. According to the result, the necessity of an external precession torque may cause slipping at lower velocities than expected if ignoring this torque.

Feasibility Study of the Form and Structure of a Ball-like Mobile Robot for Indoor Environments

In this paper the suitability of the form and structure of a new robot for indoor environments is presented and evaluated. The robot, Robolver, has a spherical outer casing which can be opened to have the halves of the casing function as wheels. The possible advantages and problem areas envisioned resulting from the robots design are identified and analyzed. Corresponding solutions for basic navigation of Robolver have been programmed and implemented, suggesting the feasibility of the design