Thilo Kerscher

Evaluation of the Dynamic Model of Fluidic Muscles using Quick-Release

By using artificial muscles in robotics one can use the analogy of the biological motor for locomotion or manipulation. There are a lot of advantages like the passive damping, good power-weight ratio and usage in rough environments. The main drawback of this muscle is that their dynamic behavior is highly nonlinear. Due to this a deep knowledge of the muscle properties and behaviors is needed to use the artificial muscle in robotics. By using the different published muscle models and our own experience we developed an advanced model for the muscle force. To validate this model a set-up like the well known quick-release test for biological muscles is used. In the future the advanced model of the fluidic muscle will help to improve the behavior of the robot PANTER and is the first step in building a biomechanical inspired two-legged robot that is able to run and walk elastically

Design and kinematics of a biologically-inspired leg for a six-legged walking machine

Legged locomotion is a fascinating form of motion. Almost all legged robotic systems are biologically-inspired by some kind of role model. The stick insect and cockroach are two of the most popular role models in the field of six-legged walking robots. Although, their legs have at least four degrees of freedom, most robotic systems, which are biologically-inspired by these insects, come along with only three joints in each leg. In this paper we will present a new leg design with four degrees of freedom for the six-legged walking machine LAURON. This enlarges the workspace of our leg significantly compared to previous leg generations and makes it very similar to the leg of the stick insect. With the additional rotational fourth joint the kinematic structure becomes redundant. The inverse kinematics for this redundant structure is solved in a very efficient way by benefiting from the orientational redundancy.

Joint control of the six-legged robot AirBug driven by fluidic muscles

Pneumatic muscles as actuators offer several advantages due to their performance weight relation or to the passive compliance of this type of actuators. Passive compliance is an important component for the control of locomotion in rough terrain to absorb the power stroke energy. This paper presents the mechatronics of a six-legged insect-like robot AirBug with pneumatic muscles as actuators. The main focus lies on the control concept of the antagonistic actuators.

Biologically inspired walking machines: design, control and perception.

This article presents a set of methods used to support the design and control of biologically inspired walking machines. Starting with a description of the general system design idea, an example for the design of the mechanical construction, a computer supported design procedure for the control architecture and the description of a three-dimensional world model to be used as knowledge base is given. The focus of this paper is on the engineering and integration process and the interrelation between the different phases of the design process.

Universal Controller Module (UCoM) - component of a modular concept in robotic systems

At our institute we built a variety of robots. As these robots are quite different as well in size, shape and in actuation principle it would be very time consuming and inefficient to build a computer and hardware architecture especially tailored to the specific robot. In this paper it will be described how common aspects in robot control can be identified and how a modular software framework and a respective computer architecture can be mapped to modular components on the hardware side. A decentralized computer architecture based on embedded PC systems connected to local controller modules via CAN-bus was developed. The requirements and restrictions that led to the development of these controller modules and their associated power amplifier boards will be described.

Proactive avoidance of moving obstacles for a service robot utilizing a behavior-based control

A main challenge in the application of service robotics is safe and reliable navigation of robots in human everyday environments. Supermarkets, which are chosen here as an example, pose a challenging scenario because they usually have a cluttered and nested character. The robot has to avoid collisions with static and even with moving obstacles while interacting with nearby humans or a dedicated user respectively. This paper presents a hierarchical approach for the proactive avoidance of moving objects as it is used on the robot shopping trolley InBOT. The behavior-based control (bbc) of InBOT is extended by a reflex and a reactive behavior to ensure adequate reaction times when confronted with a possible collision. On top of the bbc a spatio-temporal planner is situated which is able to predict environmental changes and therefore can generate a safe movement sequence accordingly.

Towards automatic manipulation action planning for service robots

A service robot should be able to automatically plan manipulation actions to help people in domestic environments. Following the classic senseplan-act cycle, in this paper we present a planning system based on a symbolic planner, which can plan feasible manipulation actions and execute it on a service robot. The approach consists of five steps. Scene Mapping formulates object relations from the current scene for the symbolic planner. Discretization generates discretized symbols for Planning. The planned manipulation actions are checked by Verification, so that it is guaranteed that they can be performed by the robot during Execution. Experiments of planned pick-and-place and pour-in tasks on real robot show the feasibility of our method.

Autonomous grasp and manipulation planning using a ToF camera

A time-of-flight camera can help a service robot to sense its 3D environment. In this paper, we introduce our methods for sensor calibration and 3D data segmentation to use it to automatically plan grasps and manipulation actions for a service robot. Impedance control is intensively used to further compensate the modeling error and to apply the computed forces. The methods are further demonstrated in three service robotic applications. Sensor-based motion planning allows the robot to move within dynamic and cluttered environment without collision. Unknown objects can be detected and grasped. In the autonomous ice cream serving scenario, the robot captures the surface of ice cream and plans a manipulation trajectory to scoop a portion of ice cream.

Graspability: A description of work surfaces for planning of robot manipulation sequences

For complex manipulation with multiple objects a service robot needs information about the structure of its environment including how and where it can manipulate in it. For this purpose, we introduce the Graspability. It is a measure describing the quality of a pose in Cartesian space for grasping or placing an object. The graspability considers kinematic reachability for a grasping robot and available grasps for the object. It is based on the assumption, that in manipulation tasks, objects tend to be located on a planar surfaces and have to be graspable from that plane. based on that assumption, we develop a discrete map of the environment which enables the use of the graspability in an autonomous planning system for complex manipulation tasks with multiple objects. Generated manipulation actions are evaluated on a real robot.

Adaptation of a six-legged walking robot to its local environment

Walking in rough and unstructured terrain with a legged robot remains to be a challenging task, not only regarding the construction of a robust walking machine, but also looking at the control of such a complex system. Walking robots have the ability to climb over obstacles and can also walk fast in flat terrain. This is possible because the control parameters are adapted to the surrounding terrain. For example, the swing height has to correspond with the obstacle height, elsewise the robot cannot walk over these obstacles. An adaptation of the control parameters according to the environment can be realised in different ways. If there is no environment model present, the robot can only rely on its sensor systems trying to react to influences from the environment. Only the use of an environment model can enable the robot to interact more intelligently with the environment and adapt its parameters in advance. In this way, the robot can avoid many collisions, which speeds up the walking process. In the example, this would mean to increase the swing height and therefore modify the footpoint trajectory with the aim to overstep the obstacle. Because the swing height is only one parameter among many others, it is obvious how expedient an environment model is for a complex walking robot like LAURON.