Mats Isaksson

Extending an industrial robot controller: implementation and applications of a fast open sensor interface

This paper describes the design and implementation of a platform for fast external sensor integration in an industrial robot control system. As an application and motivating example, the implementation of force controlled grinding and deburring within the AUTOFETT-project (EU Growth Programme) is reported.

Improving the kinematic performance of the SCARA-Tau PKM

One well acknowledged drawback of traditional parallel kinematic machines (PKMs) is that the ratio of accessible workspace to robot footprint is small for these structures. This is most likely a contributing reason why relatively few PKMs are used in industry today. The SCARA-Tau structure is a parallel robot concept designed with the explicit goal of overcoming this limitation and developing a PKM with a workspace similar to that of a serial type robot of the same size. This paper shows for the first time how a proposed variant of the SCARA-Tau PKM can improve the usability of this robot concept further by significantly reducing the dependence between tool platform position and orientation of the original concept. The inverse kinematics of the proposed variant is derived and a comparison is made between this structure and the original SCARA-Tau concept, both with respect to platform orientation changes and workspace.

Workspace and Sensitivity Analysis of a Novel Nonredundant Parallel SCARA Robot Featuring Infinite Tool Rotation

As demonstrated by the exceptionally successful Delta robot, parallel kinematics Schönflies motion generators (PKSMG) exhibit several advantages over their serial counterparts. Despite its success, the Delta robot suffers from several shortcomings, including a bulky framework and a small workspace-to-footprint ratio. Another drawback is that the kinematic chain generating tool rotation suffers from low torsional stiffness. This letter presents a novel architecture for a nonredundant PKSMG providing infinite tool rotation and an extensive positioning workspace. The workspace and kinematic performance of the proposed architecture are analysed in detail.

Workspace Analysis of a Novel Six-Degrees-of-Freedom Parallel Manipulator With Coaxial Actuated Arms

Parallel manipulators possess several advantages compared to serial robots, including the possibilities for high acceleration and high accuracy positioning of the manipulated platform. However, the majority of all proposed parallel mechanisms suffer from the combined drawbacks of a small positional workspace in relation to the manipulator footprint and a limited range of rotations of the manipulated platform. This paper analyses a recently proposed six-degrees-of-freedom parallel mechanism that aims to address both these issues while maintaining the traditional advantages of a parallel mechanism. The investigated manipulator consists of six actuated coaxial upper arms that are allowed to rotate indefinitely around a central cylindrical base column and a manipulated platform where five of the six joint positions are collinear. The axis-symmetric arm system leads to an extensive positional workspace while the proposed link arrangement increases the range of achievable platform rotations. The manipulator workspace is analyzed in detail and two methods to further increase the rotational workspace are presented. It is shown that the proposed manipulator has the possibility of a nonsingular transition of assembly modes, which extends the usable workspace. Furthermore, it is demonstrated how an additional kinematic chain can be utilized to achieve infinite platform rotation around one platform axis. By introducing additional mobility in the manipulated platform, a redundantly actuated mechanism is avoided.

Parallel Manipulators With a Rotation-Symmetric Arm System

Parallel manipulators with a rotation-symmetric arm system possess all the typical advantages of parallel robots, such as high acceleration and high-accuracy positioning. Contrary to the majority of proposed parallel manipulators, the rotation-symmetric arm system leads to a large workspace in relation to the footprint of the manipulator. This paper focuses on a subclass of these manipulators with additional favorable qualities, including low inertia and high eigenfrequencies. These qualities are achieved using only 5-DOF lower arm links and by mounting all actuators on the nonmoving base column of the manipulator. The common feature of all previously proposed manipulators in this subclass is identified and several novel 3-DOF and 4-DOF members are introduced.

A family of planar parallel manipulators

A family of planar parallel manipulators is investigated and some novel members are proposed. The common feature of the studied manipulators is that the rotation axes of the actuated arms coincide. This feature makes it possible to rotate the whole arm system an infinite number of revolutions around the center of the manipulator. The result is a large workspace in relation to the footprint. Both 2- and 3-DOF variants are presented and the suitability of this family of manipulators for kinematic analysis is demonstrated. Thus, different methods to find optimal manipulability with respect to platform positioning and rotation have been analyzed.

A Consensus-Based Framework for Distributed Bundle Adjustment

In this paper we study large-scale optimization problems in multi-view geometry, in particular the Bundle Adjustment problem. In its conventional formulation, the complexity of existing solvers scale poorly with problem size, hence this component of the Structure-from-Motion pipeline can quickly become a bottle-neck. Here we present a novel formulation for solving bundle adjustment in a truly distributed manner using consensus based optimization methods. Our algorithm is presented with a concise derivation based on proximal splitting, along with a theoretical proof of convergence and brief discussions on complexity and implementation. Experiments on a number of real image datasets convincingly demonstrates the potential of the proposed method by outperforming the conventional bundle adjustment formulation by orders of magnitude.

Pseudoconvex Proximal Splitting for L-infinity Problems in Multiview Geometry

In this paper we study optimization methods for minimizing large-scale pseudoconvex L∞ problems in multiview geometry. We present a novel algorithm for solving this class of problem based on proximal splitting methods. We provide a brief derivation of the proposed method along with a general convergence analysis. The resulting meta-algorithm requires very little effort in terms of implementation and instead makes use of existing advanced solvers for non-linear optimization. Preliminary experiments on a number of real image datasets indicate that the proposed method experimentally matches or outperforms current state-of-the-art solvers for this class of problems.

Motion/Force Transmission Analysis of Parallel Mechanisms With Planar Closed-Loop Subchains

Singularities are one of the most important issues affecting the performance of parallel mechanisms. A parallel mechanism with less than six degrees of freedom (6DOF) is classed as having lower mobility. In addition to input–output singularities, such mechanisms potentially suffer from singularities among their constraints. Furthermore, the utilization of closed-loop subchains (CLSCs) may introduce additional singularities, which can strongly affect the motion/force transmission ability of the entire mechanism. In this paper, we propose a technique for the analysis of singularities occurring within planar CLSCs, along with a finite, dimensionless, frame invariant index, based on screw theory, for examining the closeness to these singularities. The integration of the proposed index with existing performance measures is discussed in detail and exemplified on a prototype industrial parallel mechanism.

Reconfigurable multipurpose haptic interface

Complex planning tasks require substantial cognitive resources. Supporting planning tasks through enabling embodied interaction and providing multisensory feedback may reduce the cognitive load. We developed Sensators: interactive tangible objects to be used on multi-touch tables which provide both. In our demonstration, the user can experience the effect of these Sensators in planning a route through a virtual supermarket using touch-screen and passive Sensators (no feedback) or active Sensators providing multisensory feedback.This paper presents a low-cost haptic interface providing four different kinematic configurations. The different configurations are achieved using two Phantom Omni haptic devices combined with a series of clip-on attachments. Aside from the flexibility to easily reconfigure the interface, three of the four configurations provide functionality which is either not readily available or is cost prohibitive for many applications.Systematic biases have been found when matching haptic and visual locations. In this demo we can show two things; first we can show that these biases are similar when pointing at a visual target with the index finger or with a handle in a power grip. Second, we show that intermodal biases are not simply the result of a mismatch between the senses and that the transformations of the position information between modalities (and hands) are not simply reversible.In this paper we present a digital coach for runners that provides feedback in an intuitive way, without interrupting the athletes running flow. This is done by giving vibration pulses in combination with visual led feedback. The digital coach is built into a wristband with GPS module, vibration motor and several LEDs. The digital coach is given a personality model according to the DISC coaching model. From the GPS data collected the digital coach should identify which style gives the best results for the athlete.Vibrotactile texture stimuli have commonly been used to produce sensations of roughness. The extension of such stimuli to other textural modalities enhances their applicability. We found that laterally asymmetric vibrotactile stimuli cause a sensation of friction rather than vibration. When a vibrotactile contactor moves in one direction, it sticks to the finger pad and induces lateral skin stretch. In contrast, when the contactor moves in the other direction, it slips because of its quick motion and induces little skin stretch. As a result, humans experience frictional sensations in scanning vibrating contactors with their fingertips. We examined participants’ subjective responses and measured interactive forces between the finger pad and the contactor. Both perceptual and physical experiments corroborated the hypothesis of the production of a sensation of friction. Laterally asymmetric vibrotactile stimuli increased stretching of the finger pad skin and increased the sensation of friction.