Use of a Force-Torque Sensor for Self-Calibration of a 6-DOF Medical Robot.

The aim of this paper is to improve the position accuracy of a six degree of freedom medical robot. The improvement in accuracy is achieved without the use of any external measurement device. Instead, this work presents a novel calibration approach based on using an embedded force-torque sensor to identify the robot's kinematic parameters and thereby enhance the positioning accuracy. A simulation study demonstrated that our calibration approach is effective, whether or not any measurement noise is present: the position error is improved, inside the robot target workspace, from 12 mm to 0.320 mm, for the maximum values, and from 9 mm to 0.2771 mm, for the mean errors.

A Robotic Ultrasound Scanner for Automatic Vessel Tracking and Three-Dimensional Reconstruction of B-Mode Images.

Locating and evaluating the length and severity of a stenosis is very important for planning adequate treatment of peripheral arterial disease (PAD). Conventional ultrasound (US) examination cannot provide maps of entire lower limb arteries in 3-D. We propose a prototype 3D-US robotic system with B-mode images, which is nonionizing, noninvasive, and is able to track and reconstruct a continuous segment of the lower limb arterial tree between the groin and the knee. From an initialized cross-sectional view of the vessel, automatic tracking was conducted followed by 3D-US reconstructions evaluated using Hausdorff distance, cross-sectional area, and stenosis severity in comparison with 3-D reconstructions with computed tomography angiography (CTA). A mean Hausdorff distance of 0.97 ± 0.46 mm was found in vitro for 3D-US compared with 3D-CTA vessel representations. To evaluate the stenosis severity in vitro, 3D-US reconstructions gave errors of 3%-6% when compared with designed dimensions of the phantom, which are comparable to 3D-CTA reconstructions, with 4%-13% errors. The in vivo system's feasibility to reconstruct a normal femoral artery segment of a volunteer was also investigated. These results encourage further ergonomic developments to increase the robot's capacity to represent lower limb vessels in the clinical context.

A new dynamic model of the wheelchair propulsion on straight and curvilinear level-ground paths.

Independent-roller ergometers (IREs) are commonly used to simulate the behaviour of a wheelchair propelled in a straight line. They cannot, however, simulate curvilinear propulsion. To this effect, a motorised wheelchair ergometer could be used, provided that a dynamic model of the wheelchair-user system propelled on straight and curvilinear paths (WSC) is available. In this article, we present such a WSC model, its parameter identification procedure and its prediction error. Ten healthy subjects propelled an instrumented wheelchair through a controlled path. Both IRE and WSC models estimated the rear wheels' velocities based on the users' propulsive moments. On curvilinear paths, the outward wheel shows root mean square (RMS) errors of 13% in an IRE vs 8% in a WSC. The inward wheel shows RMS errors of 21% in an IRE vs 11% in a WSC. Differences between both models are highly significant (p < 0.001). A wheelchair ergometer based on this new WSC model will be more accurate than a roller ergometer when simulating wheelchair propulsion in tight environments, where many turns are necessary.

A new dynamic model of the manual wheelchair for straight and curvilinear propulsion.

Due to their mechanical design, current wheelchair ergometers cannot simulate the behaviour of a wheelchair propelled on curvilinear paths. This is because they implement a dynamic model of the Wheelchair-user system propelled on Straight Line only (WSL). In this paper, we present a new dynamic model of the Wheelchair-user propelled on Straight and Curvilinear paths (WSC), along with a characterization method based on measurements recorded on the field. Other than measured geometrical constants and kinetic/kinematic data from instrumented wheels, no information about the dynamic parameters such as the system's mass and its moment of inertia are necessary. The accuracy of the new WSC model was compared with the WSL model. To this end, ten subjects propelled an instrumented wheelchair following straight and curvilinear patterns. The recorded kinetics were fed to both models, and their estimated kinematics were compared to the recorded ones. For the curvilinear patterns, the RMS relative error between the estimated and measured rear wheels velocities over a complete push cycle are lower for the WSC model than for the WSL model. Outward wheel: 7.98% (WSC) vs 12.98% (WSL). Inward wheel: 10.76% (WSC) vs 20.73% (WSL).

Performance evaluation of a medical robotic 3D-ultrasound imaging system.

3D-ultrasound (US) imaging systems offer many advantages such as convenience, low operative costs and multiple scanning options. Most 3D-US freehand tracking systems are not optimally adapted for the quantification of lower limb arterial stenoses because their performance depends on the scanning length, on ferro-magnetic interferences or because they require a constant line of sight with the US probe. Robotic systems represent a promising alternative since they can control and standardize the 3D-US acquisition process for large scanning distances without requiring a specific line of sight. The performance of a new prototype medical robot, in terms of positioning and inter-target accuracies (i.e., difference between measurements and ground truth values) was evaluated with a lower-limb mimicking phantom throughout the robot workspace. The teach/replay repeatability (i.e., difference between taught and replayed points) was also assessed. A mean positioning accuracy between 0.46 mm and 0.75 mm was found on all scanning zones. The mean inter-target distance accuracy varied between 0.26 mm and 0.61 mm. Teach/replay repeatability below 0.20mm was also obtained. Additionally, a 3D reconstruction of in-vitro stenoses was performed with the robotic US scanner. The quantification error of a 80% area reduction (AR) stenosis was 3.0%, whereas it was -0.9% for a less severe 75% AR stenosis. Altogether, these results suggest that the robot may be of value for the clinical evaluation of lower limb vessels over long and tortuous segments starting from the iliac artery down to the popliteal artery below the knee.