One of the major outcomes of the EPSRC/British Aerospace supported project “Enabling Tactile Technology Environments”, was the Reactabot, a three degree of freedom force feedback device which provides tactual/kinaesthetic feedback to an operator via a surrogate object. Systems of this nature exhibit unwanted oscillatory behaviour and eventually instability if the virtual mass is reduced to too low a value, corresponding to raising the loop gain too high. The onset of this behaviour is found to be operator dependent. This paper studies the phenomenon in detail, modelling both the open loop system and human operator in the feedback path. It is shown that the variation between operators, allied with the unwanted but inevitable phase lags in the open loop system, cause the undesirable behaviour and suggestions are made to minimise their effect

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We present a new device aimed at being used for upper limb rehabilitation. Our main focus was to design a robot capable of working in both the passive mode (i.e. the robot shall be strong enough to generate human-like movements while guiding the weak arm of a patient) and the active mode (i.e. the robot shall be able of following the arm without disturbing human natural motion). This greatly challenges the design, since the system shall be reversible and lightweight while providing human compatible strength, workspace and speed. The solution takes the form of an orthotic structure, which allows control of human arm redundancy contrarily to clinically available upper limb rehabilitation robots. It is equipped with an innovative transmission technology, which provides both high gear ratio and fine reversibility. In order to evaluate the device and its therapeutic efficacy, we compared several series of pointing movements in healthy subjects wearing and not wearing the orthotic device. In this way, we could assess any disturbing effect on normal movements. Results show that the main movement characteristics (direction, duration, bell shape profile) are preserved.

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Post-stroke robot-aided neurorehabilitation is an emerging research field, aiming to improve the intensity and the effectiveness of post-stroke rehabilitation protocols by using robotic technology and virtual reality. One classification that has been proposed for therapy robots is between exoskeletons and end-effector based machines. The latter are those devices whose interaction with the patient’s arm takes place at the end-effector level. This paper presents the design of two novel end-effector based robots for upper-limb rehabilitation, named Sophia-4 and Sophia-3. Although the devices are based on a common concept (the cable-drive actuation over a planar workspace), the latter differs from the former by the number of employed cables (4 and 3, respectively), and, by several design solutions, such as the introduction of a moving pulley-block to enhance workspace and a tilting table to better target the patient’s shoulder. Both mechanical and control system design are addressed and a comparison of performances is presented.

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A path-planning algorithm for encountered-type haptic devices that render multiple virtual objects in 3D space is proposed. To render multiple virtual objects with a single haptic device, the following two behaviors must be realized: (i) the device should move to the target object location in advance of the user’s hand so that the user can encounter it; (ii) otherwise, the device should keep away from the user’s hand, avoiding an unexpected collision. To realize such a consistent encounter, the user’s hand motion must be tracked. The proposed algorithm determines the device location based on the minimum distance problem between a point (the user’s hand) and a convex polyhedron constructed from the reference points of multiple objects. An automobile virtual control panel was constructed using an encountered-type haptic device in which the proposed path-planning algorithm was implemented. The validity of the proposed algorithm was confirmed and the required performances, such as the device speed and the accuracy of hand tracking were evaluated.

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