Dieter Schramm

A real-time capable force calculation algorithm for redundant tendon-based parallel manipulators

Tendon-based parallel manipulators with n d.o.f. use at least m = n + 1 tendons to guide the end effector along a given trajectory. Since tendons can only transmit limited and tractive forces, it is essential to apply a valid tendon force distribution. Due to safety and precision requirements, a combined position and force control is needed where the force calculation delivers the desired tendon force distributions. The high dynamic potential of the robot demands for realtime capable algorithms. To avoid steps in the motor torques the calculated tension force distributions also have to be continuous along the trajectory. In this paper, a new algorithm for tendon force distribution calculations capable for usage on a realtime system is proposed and its continuity is proven.

Wire Robots Part I: Kinematics, Analysis & Design

One drawback of classical parallel robots is their limited workspace, mainly due to the limitation of the stroke of linear actuators. Parallel wire robots (also known as Tendon-based Steward platforms or cable robots) face this problem through substitution of the actuators by wires (or tendons, cables, . . .). Tendon-based Steward platforms have been proposed in (Landsberger & Sheridan, 1985). Although these robots share the basic concepts of classical parallel robots, there are some major differences:

Design and Control of the Quadruped Walking Robot ALDURO

Alduro is a four-legged walking robot. Its main goal is to operate in rugged terrain, translating the cartesian operator commands (joystick) into actuator space by coordinating the legs according to the users wish. At the same time static stability has to be guaranteed, obstacles have to be avoided and the posture of the main body kept. This requires an elaborate motion coordination and controller software. One possible way to organise this is described here: by isolating the physical robot from the motion generation (hardware abstraction layer), by using concurrent behaviours for motion generation and by strict modularisation of the software. The selected tools and realtime operating system are described in the last sections.

Modeling of a Thermoelectric Generator for Thermal Energy Regeneration in Automobiles

In the field of passenger transportation a reduction of the consumption of fossil fuels has to be achieved by any measures. Advanced designs of internal combustion engine have the potential to reduce CO2 emissions, but still suffer from low efficiencies in the range from 33% to 44%. Recuperation of waste heat can be achieved with thermoelectric generators (TEGs) that convert heat directly into electric energy, thus offering a less complicated setup as compared with thermodynamic cycle processes. During a specific driving cycle of a car, the heat currents and temperature levels of the exhaust gas are dynamic quantities. To optimize a thermoelectric recuperation system fully, various parameters have to be tested, for example, the electric and thermal conductivities of the TEG and consequently the heat absorbed and rejected from the system, the generated electrical power, and the system efficiency. A Simulink model consisting of a package for dynamic calculation of energy management in a vehicle, coupled with a model of the thermoelectric generator system placed on the exhaust system, determines the drive-cycle-dependent efficiency of the heat recovery system, thus calculating the efficiency gain of the vehicle. The simulation also shows the temperature drop at the heat exchanger along the direction of the exhaust flow and hence the variation of the voltage drop of consecutively arranged TEG modules. The connection between the temperature distribution and the optimal electrical circuitry of the TEG modules constituting the entire thermoelectric recuperation system can then be examined. The simulation results are compared with data obtained from laboratory experiments. We discuss error bars and the accuracy of the simulation results for practical thermoelectric systems embedded in cars.

A new force calculation algorithm for tendon-based parallel manipulators

Completely and redundantly restraint tendon-based Stewart platforms demand for an appropriate distribution of tendon forces to control the platform on a given trajectory. Thus, position control has to be extended by a tendon force controller which generates continuous and feasible force values. The computation of such force distributions can be formulated as a constrained optimization problem. Solving the problem is numerically expensive and requires an algorithm which is capable to be integrated into a realtime environment. In this paper, a new algorithm for tendon force distribution calculations capable for usage on a realtime system is proposed.

HiL simulation of electric vehicles in different usage scenarios

This paper describes the simulation of an electric vehicle drive train via a hardware in the loop (HiL) setup in combination with an interactive driving simulator based on MATLAB/Simulink. This setup provides the possibility to test the suitability of electric vehicles in different usage scenarios using a laboratory environment. Another aspect is that by a comprehensive analysis of the measurement data, system components of the drive train can be tested under realistic conditions and further developed in order to improve the efficiency of such vehicles.

Wire Robots Part II Dynamics, Control & Application

In (Bruckmann et al., 2008) the kinematics, analysis and design of wire robots were presented. This chapter focuses on control and applications of wire robots. Wire robots are a very recent area of research. Nevertheless, they are well studied and already in application (see section 5). Due to their possible lightweight structure, wire robots can operate at very high velocities. Hence, as can be seen by experiment, only positioning control using the inverse kinematics is not sufficient. In particular, slackness in the wires can be observed at highly dynamic motions. To overcome this problem, force control can be employed. In section 4 different control schemes are proposed. The required dynamical model is obtained in section 2, while for the calculation of feasible wire force distributions are proposed in section 3. Since wire robots are kinematically redundant the latter is not straightforward, but requires advanced approaches. The same holds for the control schemes, since a CRPM as well as a RRPM is a non-linear, coupled, redundant system (Ming & Higuchi, 1994).

Investigations on the Impact of Different Electric Vehicle Traction Systems in Urban Traffic

Currently electric vehicles are introduced in e.g. public transport and individual traffic in order to reduce i.a. the green house gas emissions. The main disadvantage of electric vehicles compared to vehicles with conventional drive is the shorter operating distance. In contrast this disadvantage is partially negligible in urban usage scenarios, like e.g. taxi or delivery services. This paper focuses on the simulation of electric vehicle propulsion systems using a Hardware in the Loop (HiL) model. The model consisting of components used in actual electric vehicles is scaled using Buckinghams Pi-Theorem in order to analyze the impact of different electric traction systems on the vehicles energy consumption. Thus the available operating distance of such vehicles can be optimized in urban traffic.

Maneuver prediction at intersections using cost-to-go gradients

According to the analysis of car accidents many casualties occur at intersections. As ongoing research demonstrates, Advanced Driver Assistance Systems that aim at preventing this type of accident, need to reliably predict the turning maneuver of all relevant participants in the scene. In this work an approach is introduced, which models human drivers as the optimizer of an optimal control problem with an unknown terminal state. Tracking the cost-to-go gradient to the terminal state of each driving option leads to the most plausible hypothesis. The optimal control problem itself is formulated with costs that minimize jerk, time and steering effort with good resemblance to typical human driving behavior. In combination with a simplified vehicle model this leads to a nonlinear constrained dynamic optimization problem, which is solved numerically. The performance of the proposed approach is evaluated on data obtained in a field test with promising results.

An Active Suspension System for Simulation of Ship Maneuvers in Wind Tunnels

Wind tunnels are an experimental tool to evaluate the air flow properties of vehicles in model scale and to optimize the design of aircrafts and aircraft components. Also the hydrodynamic properties of marine components like ship hulls or propulsion systems can be examined. For advanced optimization, it is necessary to guide the models along defined trajectories during the tests to vary the angle of attack. Due to their good aerodynamical properties, parallel wire robots were successfully used to perform these maneuvers in wind tunnels. Compared to aircraft hulls, marine models may be very heavy-weight (up to 150 kg). Thus, the suspension system must be very stiff to avoid vibrations. Additionally, fast maneuvers require powerful drives. On the other hand, the positioning system should not influence the air flow to ensure unaltered experimental results. In this paper, different designs are presented and discussed.