Stroke survivors may benefit from robotic assistance for relearning of functional movements. Current assistive devices are either passive, limited to only two dimensions or very powerful. However, for reach training, weight compensation and a little assistance with limited power is sufficient. We designed and evaluated a novel three-dimensional robotic manipulator, which is able to support the arm weight and assist functional reaching movements. Key points of the design are a damper-based drive train, giving an inherently safe system and its compact and lightweight design. The system is force actuated with a bandwidth of up to 2.3 Hz, which is sufficient for functional arm movements. Maximal assistive forces are 15 N for the up/down and forward/backward directions and 10 N for the left/right direction. Force tracking errors are smaller than 1.5 N for all axes and the total weight of the robot is 25 kg. Furthermore, the device has shown its benefit for increasing reaching distance in a single-case study with a stroke subject. The newly developed system has the technical ability to assist the arm during movement, which is a prerequisite for successful training of stroke survivors. Therapeutic effects of the applied assistance need to be further evaluated. However, with its inherent safety and ease of use, this newly developed system even has the potential for home-based therapeutic training after stroke.
In this work, we present a new continuously variable transmission concept: the Dual-Hemi Continuously Variable Transmission (CVT). It is designed to have properties we believe are required to apply continuously variable transmissions in robotics to their full potential. These properties are a transformation range that includes both positive and negative ratios, back-drivability under all conditions, kinematically decoupled reconfiguration, high efficiency of the transmission, and a reconfiguration mechanism requiring little work for changing the transmission ratio. The design of the Dual-Hemi CVT and a prototype realisation are discussed in detail. We show that the Dual-Hemi CVT has the aforementioned desired properties. Experiments show that the efficiency of the CVT is above 90% for a large part of the range of operation of the CVT. Significant stiction in the transmission, combined with a relatively low bandwidth for changing the transmission ratio, may cause problems when applying the DH-CVT as part of an actuator in a control loop.
A system was developed for computed tomography (CT)-guided needle placement in the thorax and abdomen, providing precise aiming of a needle guide (NG) to reach a user-specified target in a single manual insertion. The objective of this work is to present its technical design and analyze its performance in terms of placement error in air. The individual contributions to the placement error of a fiducial marker based system-to-CT registration system, a two degrees-of-freedom (2DOFs) drive system to aim the NG, and a structural link between NG and CT table were experimentally determined, in addition to the placement error of the overall system. An error contribution of 0.81 ± 0.34 mm was determined for the registration system, <1.2 mm and <3.3 mm for the drive system, and 0.35 mm and 0.43 mm for two load cases of the structural link. The overall unloaded system achieved 1.0 ± 0.25 mm and 2.6 ± 0.7 mm at 100 mm and 250 mm depth, respectively. The overall placement errors in air do not exceed the ≤5 mm error specified as a clinical user requirement for needle placement in tissue.
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