Manfred Hiller

Motion control of a tendon-based parallel manipulator using optimal tension distribution

This paper presents the motion control of a six degree-of-freedom tendon-based parallel manipulator, which moves a platform with high speed using seven cables. To control the motion of the platform along desired trajectories in space, nonlinear feedforward control laws in the cable length coordinates are used. Taking account of the effect of redundancy on actuation, the optimal tension distribution should be considered to the advantage of the control laws. Using a method based on the analysis of the workspace condition, tension constraints and limiting torque constraints of actuators, an analytical solution for optimum tension distribution was found and used to compute the force in each cable for compensation of dynamic errors. It is experimentally demonstrated that the proposed control laws reduce the energy consumption of the actuators and satisfy the path tracking accuracy.

On design of a redundant wire-driven parallel robot WARP manipulator

A redundant wire-driven parallel robot, the WARP manipulator, is a new robot mechanism which is suitable especially for high speed assembling of lightweight objects such as semiconductors. In this paper, a WARP manipulator was designed from the viewpoint of working space by considering conditions that the travelling plate must be abbe to generate arbitrary amounts of force and moment and the wires are not to be in contact. Simulation results of working space proved the validity of the design procedure described. A prototype of WARP manipulator was constructed. The kinematic parameters were calibrated for position control.

Workspace, Stiffness, Singularities and Classification of Tendon-Driven Stewart Platforms

A mathematical model for tendon-driven Stewart platform manipulators is developed. Conditions for the workspace are given, including tension limits, stiffness and singularities. It is proved that there are six classes of manipulators that exert the same wrenches all over the workspace. Simulation results of a 2-dof planar manipulator are presented.

Estimating the Controllable Workspace of Tendon-Based Stewart Platforms

The controllable workspace of a tendon-based Stewart Platform is the set of postures where forces and torques at the end-effector can be controlled. A necessary and sufficient condition is given for those postures where forces can be controlled; thus, a superset of the controllable workspace can be calculated easily. External forces are modeled as an additional tendon fixed at inifinity by introducing an unusual compactification of IRn that contains one infinitely distant point for each direction.

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.

An object-oriented approach for an effective formulation of multibody dynamics

Abstract This paper describes a new method for the modeling of the kinematics and dynamics of multibody systems, which is based on the responsibility-driven approach for object-oriented design and the concept of ‘kinetostatic transmission elements’ for mechanical modeling. As a result, a highly data-independent formulation is achieved, where the generic operations offer several analogies to general mappings from manifold theory. The implementation of the approach offers a collection of classes which resemble their real-world counterparts and which allow us to develop, by simple assembly of pre-defined objects, ‘hand-tailored’ multibody programs which are fast and can be integrated in other applications. This is illustrated by an example. Although in this paper the mathematical complexity of the underlying equations is held at a low level, it is easy to extend the method to cover graphical rendering, efficient computation techniques, and elasticity effects. These extensions will be described in future publications.

A motion base with 6-DOF by parallel cable drive architecture

This paper proposes a new type of motion base for virtual sensation of acceleration by applying a parallel cable drive architecture. It has outstanding advantages in comparison with conventional Stewart platforms. Especially, 1) rotational motion range is large; 2) the motion platform can be grounded on the floor; 3) scene projection to all the walls is possible; and 4) its redundancy of cables improves safety for cut of cables. Optimal fundamental mechanical design is performed from the viewpoint of kinematics. Simulation results show that a 3-3-2 cable configuration is one of the best designs as a motion base. The prototype developed has the maximum motion range of translation /spl plusmn/0.45 m /spl times/ /spl plusmn/0.4 m /spl times/ 1.1 m and that of rotation /spl plusmn/45/spl deg/ in roll angle, /spl plusmn/45/spl deg/ in pitch, and /spl plusmn/35/spl deg/ in yaw. It can produce acceleration 1 G for 0.8 s at its maximum, even if gravity is not used. A trajectory planning method for longer-term sensation utilizing gravity is proposed. Low-frequency component of acceleration is realized by rotational motion and high frequency is produced by translational motion. Experimental results to create virtual acceleration of a roller coaster demonstrated effectiveness of this new design.

A portable parallel manipulator for search and rescue at large-scale urban earthquakes and an identification algorithm for the installation in unstructured environments

Essential points in robotic facilities for search and rescue at large-scale urban earthquakes were investigated. A parallel robot driven by multiple cables is proposed for transfer of debris. It is portable and is assembled rapidly in destroyed houses. An identification algorithm of mechanism parameters peculiar to this portable robot was studied. On the basis of identification error analysis, optimal number of measurement points and the size of an identification reference frame were obtained.

Symbolic Processing of Multiloop Mechanism Dynamics Using Closed-Form Kinematics Solutions

This paper describes a method for the automated symbolic generation of the equations of motion of multibody systems using closed-form solutions of the kinematics at the position, velocity and acceleration levels where possible. The basic idea of the method is to employ the set of smallestindependent loops of the system as building blocks for the overall kinematics of the system. Using a geometric-algebraic approach, closed-form solutions are detected and generated for each loop where this is possible. These local solutions are then assembled at the global level, yielding a block diagram from which closed-form solutions for the overall system areproduced where possible. The equations of motion of minimal order are then generated by sums and products involving matrices from the kinematicprocessing. The resulting expressions are fully symbolic and do not contain redundant computations. The method was implemented in Mathematica and was applied to several mechanisms of practical relevance. A comparison of closed-form solutions with iterative solutions shows that the closed-formsolutions are more efficient by a factor of up to 8.

Emergency path planning for autonomous vehicles using elastic band theory

In this paper a path planning method for emergency maneuvers of autonomous vehicles is presented. The path planning method is based on the theory of elastic bands. Due to the local disturbances caused by obstacles on the nominal trajectory the elastic behavior allows sufficient flexibility of the emergency trajectory and minimal local changes of curvature. The minimization of local changes of curvature ensures the drivability of the emergency trajectory under vehicle dynamics aspect, which is also considered in this paper. The results of the described method is demonstrated for emergency situations in lane change maneuvers for autonomous vehicles.